diff --git a/core/res/res/values/config.xml b/core/res/res/values/config.xml
index 8295eb0a61719..bd7516b71f435 100644
--- a/core/res/res/values/config.xml
+++ b/core/res/res/values/config.xml
@@ -5301,6 +5301,10 @@
     <!-- Whether vertical reachability repositioning is allowed for letterboxed fullscreen apps. -->
     <bool name="config_letterboxIsVerticalReachabilityEnabled">false</bool>
 
+    <!-- Whether book mode automatic horizontal reachability positioning is allowed for letterboxed
+        fullscreen apps -->
+    <bool name="config_letterboxIsAutomaticReachabilityInBookModeEnabled">false</bool>
+
     <!-- Default horizontal position of the letterboxed app window when reachability is
         enabled and an app is fullscreen in landscape device orientation. When reachability is
         enabled, the position can change between left, center and right. This config defines the
diff --git a/core/res/res/values/symbols.xml b/core/res/res/values/symbols.xml
index f06d4371202c5..5ab902fc5ae30 100644
--- a/core/res/res/values/symbols.xml
+++ b/core/res/res/values/symbols.xml
@@ -4505,6 +4505,7 @@
   <java-symbol type="dimen" name="config_letterboxTabletopModePositionMultiplier" />
   <java-symbol type="bool" name="config_letterboxIsHorizontalReachabilityEnabled" />
   <java-symbol type="bool" name="config_letterboxIsVerticalReachabilityEnabled" />
+  <java-symbol type="bool" name="config_letterboxIsAutomaticReachabilityInBookModeEnabled" />
   <java-symbol type="integer" name="config_letterboxDefaultPositionForHorizontalReachability" />
   <java-symbol type="integer" name="config_letterboxDefaultPositionForVerticalReachability" />
   <java-symbol type="integer" name="config_letterboxDefaultPositionForBookModeReachability" />
diff --git a/services/core/java/com/android/server/wm/ActivityRecord.java b/services/core/java/com/android/server/wm/ActivityRecord.java
index e970e6a82b1aa..df13c13b208ad 100644
--- a/services/core/java/com/android/server/wm/ActivityRecord.java
+++ b/services/core/java/com/android/server/wm/ActivityRecord.java
@@ -8587,7 +8587,7 @@ final class ActivityRecord extends WindowToken implements WindowManagerService.A
         resolvedBounds.set(containingBounds);
 
         final float letterboxAspectRatioOverride =
-                mLetterboxUiController.getFixedOrientationLetterboxAspectRatio();
+                mLetterboxUiController.getFixedOrientationLetterboxAspectRatio(newParentConfig);
         final float desiredAspectRatio =
                 letterboxAspectRatioOverride > MIN_FIXED_ORIENTATION_LETTERBOX_ASPECT_RATIO
                         ? letterboxAspectRatioOverride : computeAspectRatio(parentBounds);
diff --git a/services/core/java/com/android/server/wm/LetterboxConfiguration.java b/services/core/java/com/android/server/wm/LetterboxConfiguration.java
index 37cf5bc95a23e..ec04894b1d42c 100644
--- a/services/core/java/com/android/server/wm/LetterboxConfiguration.java
+++ b/services/core/java/com/android/server/wm/LetterboxConfiguration.java
@@ -184,6 +184,10 @@ final class LetterboxConfiguration {
     // portrait device orientation.
     private boolean mIsVerticalReachabilityEnabled;
 
+    // Whether book mode automatic horizontal reachability positioning is allowed for letterboxed
+    // fullscreen apps in landscape device orientation.
+    private boolean mIsAutomaticReachabilityInBookModeEnabled;
+
     // Whether education is allowed for letterboxed fullscreen apps.
     private boolean mIsEducationEnabled;
 
@@ -277,6 +281,8 @@ final class LetterboxConfiguration {
                 R.bool.config_letterboxIsHorizontalReachabilityEnabled);
         mIsVerticalReachabilityEnabled = mContext.getResources().getBoolean(
                 R.bool.config_letterboxIsVerticalReachabilityEnabled);
+        mIsAutomaticReachabilityInBookModeEnabled = mContext.getResources().getBoolean(
+                R.bool.config_letterboxIsAutomaticReachabilityInBookModeEnabled);
         mDefaultPositionForHorizontalReachability =
                 readLetterboxHorizontalReachabilityPositionFromConfig(mContext, false);
         mDefaultPositionForVerticalReachability =
@@ -681,6 +687,14 @@ final class LetterboxConfiguration {
         return mIsVerticalReachabilityEnabled;
     }
 
+    /*
+     * Whether automatic horizontal reachability repositioning in book mode is allowed for
+     * letterboxed fullscreen apps in landscape device orientation.
+     */
+    boolean getIsAutomaticReachabilityInBookModeEnabled() {
+        return mIsAutomaticReachabilityInBookModeEnabled;
+    }
+
     /**
      * Overrides whether horizontal reachability repositioning is allowed for letterboxed fullscreen
      * apps in landscape device orientation.
@@ -697,6 +711,14 @@ final class LetterboxConfiguration {
         mIsVerticalReachabilityEnabled = enabled;
     }
 
+    /**
+     * Overrides whether automatic horizontal reachability repositioning in book mode is allowed for
+     * letterboxed fullscreen apps in landscape device orientation.
+     */
+    void setIsAutomaticReachabilityInBookModeEnabled(boolean enabled) {
+        mIsAutomaticReachabilityInBookModeEnabled = enabled;
+    }
+
     /**
      * Resets whether horizontal reachability repositioning is allowed for letterboxed fullscreen
      * apps in landscape device orientation to
@@ -717,6 +739,16 @@ final class LetterboxConfiguration {
                 R.bool.config_letterboxIsVerticalReachabilityEnabled);
     }
 
+    /**
+     * Resets whether automatic horizontal reachability repositioning in book mode is
+     * allowed for letterboxed fullscreen apps in landscape device orientation to
+     * {@link R.bool.config_letterboxIsAutomaticReachabilityInBookModeEnabled}.
+     */
+    void resetEnabledAutomaticReachabilityInBookMode() {
+        mIsAutomaticReachabilityInBookModeEnabled = mContext.getResources().getBoolean(
+                R.bool.config_letterboxIsAutomaticReachabilityInBookModeEnabled);
+    }
+
     /*
      * Gets default horizontal position of the letterboxed app window when horizontal reachability
      * is enabled.
diff --git a/services/core/java/com/android/server/wm/LetterboxUiController.java b/services/core/java/com/android/server/wm/LetterboxUiController.java
index a36b8c0e5d6af..54137eb41c5fd 100644
--- a/services/core/java/com/android/server/wm/LetterboxUiController.java
+++ b/services/core/java/com/android/server/wm/LetterboxUiController.java
@@ -801,13 +801,18 @@ final class LetterboxUiController {
     float getHorizontalPositionMultiplier(Configuration parentConfiguration) {
         // Don't check resolved configuration because it may not be updated yet during
         // configuration change.
-        boolean bookMode = isDisplayFullScreenAndInPosture(
-                DeviceStateController.DeviceState.HALF_FOLDED, false /* isTabletop */);
+        boolean bookModeEnabled = isFullScreenAndBookModeEnabled();
         return isHorizontalReachabilityEnabled(parentConfiguration)
                 // Using the last global dynamic position to avoid "jumps" when moving
                 // between apps or activities.
-                ? mLetterboxConfiguration.getHorizontalMultiplierForReachability(bookMode)
-                : mLetterboxConfiguration.getLetterboxHorizontalPositionMultiplier(bookMode);
+                ? mLetterboxConfiguration.getHorizontalMultiplierForReachability(bookModeEnabled)
+                : mLetterboxConfiguration.getLetterboxHorizontalPositionMultiplier(bookModeEnabled);
+    }
+
+    private boolean isFullScreenAndBookModeEnabled() {
+        return isDisplayFullScreenAndInPosture(
+                DeviceStateController.DeviceState.HALF_FOLDED, false /* isTabletop */)
+                && mLetterboxConfiguration.getIsAutomaticReachabilityInBookModeEnabled();
     }
 
     float getVerticalPositionMultiplier(Configuration parentConfiguration) {
@@ -822,12 +827,14 @@ final class LetterboxUiController {
                 : mLetterboxConfiguration.getLetterboxVerticalPositionMultiplier(tabletopMode);
     }
 
-    float getFixedOrientationLetterboxAspectRatio() {
+    float getFixedOrientationLetterboxAspectRatio(@NonNull Configuration parentConfiguration) {
+        // Don't resize to split screen size when half folded if letterbox position is centered
         return isDisplayFullScreenAndSeparatingHinge()
-                ? getSplitScreenAspectRatio()
-                : mActivityRecord.shouldCreateCompatDisplayInsets()
-                    ? getDefaultMinAspectRatioForUnresizableApps()
-                    : getDefaultMinAspectRatio();
+                    && getHorizontalPositionMultiplier(parentConfiguration) != 0.5f
+                        ? getSplitScreenAspectRatio()
+                        : mActivityRecord.shouldCreateCompatDisplayInsets()
+                            ? getDefaultMinAspectRatioForUnresizableApps()
+                            : getDefaultMinAspectRatio();
     }
 
     private float getDefaultMinAspectRatioForUnresizableApps() {
@@ -889,7 +896,8 @@ final class LetterboxUiController {
             return;
         }
 
-        boolean isInFullScreenBookMode = isDisplayFullScreenAndSeparatingHinge();
+        boolean isInFullScreenBookMode = isDisplayFullScreenAndSeparatingHinge()
+                && mLetterboxConfiguration.getIsAutomaticReachabilityInBookModeEnabled();
         int letterboxPositionForHorizontalReachability = mLetterboxConfiguration
                 .getLetterboxPositionForHorizontalReachability(isInFullScreenBookMode);
         if (mLetterbox.getInnerFrame().left > x) {
diff --git a/services/core/java/com/android/server/wm/WindowManagerShellCommand.java b/services/core/java/com/android/server/wm/WindowManagerShellCommand.java
index b75c9603ceed6..966ac63fd1c4f 100644
--- a/services/core/java/com/android/server/wm/WindowManagerShellCommand.java
+++ b/services/core/java/com/android/server/wm/WindowManagerShellCommand.java
@@ -966,6 +966,10 @@ public class WindowManagerShellCommand extends ShellCommand {
                     runSetBooleanFlag(pw, mLetterboxConfiguration
                             ::setIsVerticalReachabilityEnabled);
                     break;
+                case "--isAutomaticReachabilityInBookModeEnabled":
+                    runSetBooleanFlag(pw, mLetterboxConfiguration
+                            ::setIsAutomaticReachabilityInBookModeEnabled);
+                    break;
                 case "--defaultPositionForHorizontalReachability":
                     runSetLetterboxDefaultPositionForHorizontalReachability(pw);
                     break;
@@ -1168,6 +1172,7 @@ public class WindowManagerShellCommand extends ShellCommand {
             mLetterboxConfiguration.resetLetterboxHorizontalPositionMultiplier();
             mLetterboxConfiguration.resetIsHorizontalReachabilityEnabled();
             mLetterboxConfiguration.resetIsVerticalReachabilityEnabled();
+            mLetterboxConfiguration.resetEnabledAutomaticReachabilityInBookMode();
             mLetterboxConfiguration.resetDefaultPositionForHorizontalReachability();
             mLetterboxConfiguration.resetDefaultPositionForVerticalReachability();
             mLetterboxConfiguration.resetIsEducationEnabled();
@@ -1203,6 +1208,8 @@ public class WindowManagerShellCommand extends ShellCommand {
                     + mLetterboxConfiguration.getIsHorizontalReachabilityEnabled());
             pw.println("Is vertical reachability enabled: "
                     + mLetterboxConfiguration.getIsVerticalReachabilityEnabled());
+            pw.println("Is automatic reachability in book mode enabled: "
+                    + mLetterboxConfiguration.getIsAutomaticReachabilityInBookModeEnabled());
             pw.println("Default position for horizontal reachability: "
                     + LetterboxConfiguration.letterboxHorizontalReachabilityPositionToString(
                             mLetterboxConfiguration.getDefaultPositionForHorizontalReachability()));
diff --git a/services/tests/wmtests/src/com/android/server/wm/SizeCompatTests.java b/services/tests/wmtests/src/com/android/server/wm/SizeCompatTests.java
index 671b27584fccb..3e423c4d29ecf 100644
--- a/services/tests/wmtests/src/com/android/server/wm/SizeCompatTests.java
+++ b/services/tests/wmtests/src/com/android/server/wm/SizeCompatTests.java
@@ -3664,7 +3664,6 @@ public class SizeCompatTests extends WindowTestsBase {
 
     @Test
     public void testUpdateResolvedBoundsVerticalPosition_tabletop() {
-
         // Set up a display in portrait with a fixed-orientation LANDSCAPE app
         setUpDisplaySizeWithApp(1400, 2800);
         mActivity.mDisplayContent.setIgnoreOrientationRequest(true /* ignoreOrientationRequest */);
@@ -3686,16 +3685,15 @@ public class SizeCompatTests extends WindowTestsBase {
         setFoldablePosture(false /* isHalfFolded */, false /* isTabletop */);
 
         assertEquals(letterboxNoFold, mActivity.getBounds());
-
     }
 
     @Test
-    public void testUpdateResolvedBoundsHorizontalPosition_book() {
-
+    public void testUpdateResolvedBoundsHorizontalPosition_bookModeEnabled() {
         // Set up a display in landscape with a fixed-orientation PORTRAIT app
         setUpDisplaySizeWithApp(2800, 1400);
         mActivity.mDisplayContent.setIgnoreOrientationRequest(true /* ignoreOrientationRequest */);
-        mActivity.mWmService.mLetterboxConfiguration.setLetterboxHorizontalPositionMultiplier(
+        mWm.mLetterboxConfiguration.setIsAutomaticReachabilityInBookModeEnabled(true);
+        mWm.mLetterboxConfiguration.setLetterboxHorizontalPositionMultiplier(
                 1.0f /*letterboxVerticalPositionMultiplier*/);
         prepareUnresizable(mActivity, SCREEN_ORIENTATION_PORTRAIT);
 
@@ -3713,7 +3711,28 @@ public class SizeCompatTests extends WindowTestsBase {
         setFoldablePosture(false /* isHalfFolded */, false /* isTabletop */);
 
         assertEquals(letterboxNoFold, mActivity.getBounds());
+    }
 
+    @Test
+    public void testUpdateResolvedBoundsHorizontalPosition_bookModeDisabled_centered() {
+        // Set up a display in landscape with a fixed-orientation PORTRAIT app
+        setUpDisplaySizeWithApp(2800, 1400);
+        mActivity.mDisplayContent.setIgnoreOrientationRequest(true /* ignoreOrientationRequest */);
+        mWm.mLetterboxConfiguration.setLetterboxHorizontalPositionMultiplier(0.5f);
+        prepareUnresizable(mActivity, 1.75f, SCREEN_ORIENTATION_PORTRAIT);
+
+        Rect letterboxNoFold = new Rect(1000, 0, 1800, 1400);
+        assertEquals(letterboxNoFold, mActivity.getBounds());
+
+        // Make the activity full-screen
+        mTask.setWindowingMode(WINDOWING_MODE_FULLSCREEN);
+
+        // Stay centered and bounds don't change
+        setFoldablePosture(true /* isHalfFolded */, false /* isTabletop */);
+        assertEquals(letterboxNoFold, mActivity.getBounds());
+
+        setFoldablePosture(false /* isHalfFolded */, false /* isTabletop */);
+        assertEquals(letterboxNoFold, mActivity.getBounds());
     }
 
     private void setFoldablePosture(ActivityRecord activity, boolean isHalfFolded,