diff --git a/services/core/java/com/android/server/wm/LetterboxUiController.java b/services/core/java/com/android/server/wm/LetterboxUiController.java
index 67e188fa90454..d2f62da0b26f5 100644
--- a/services/core/java/com/android/server/wm/LetterboxUiController.java
+++ b/services/core/java/com/android/server/wm/LetterboxUiController.java
@@ -724,6 +724,7 @@ final class LetterboxUiController {
      *   <li>Activity is portrait-only.
      *   <li>Fullscreen window in landscape device orientation.
      *   <li>Horizontal Reachability is enabled.
+     *   <li>Activity fills parent vertically.
      * </ul>
      */
     private boolean isHorizontalReachabilityEnabled(Configuration parentConfiguration) {
@@ -731,10 +732,14 @@ final class LetterboxUiController {
                 && parentConfiguration.windowConfiguration.getWindowingMode()
                         == WINDOWING_MODE_FULLSCREEN
                 && (parentConfiguration.orientation == ORIENTATION_LANDSCAPE
-                && mActivityRecord.getOrientationForReachability() == ORIENTATION_PORTRAIT);
+                        && mActivityRecord.getOrientationForReachability() == ORIENTATION_PORTRAIT)
+                // Check whether the activity fills the parent vertically.
+                && parentConfiguration.windowConfiguration.getBounds().height()
+                        == mActivityRecord.getBounds().height();
     }
 
-    private boolean isHorizontalReachabilityEnabled() {
+    @VisibleForTesting
+    boolean isHorizontalReachabilityEnabled() {
         return isHorizontalReachabilityEnabled(mActivityRecord.getParent().getConfiguration());
     }
 
@@ -746,6 +751,7 @@ final class LetterboxUiController {
      *   <li>Activity is landscape-only.
      *   <li>Fullscreen window in portrait device orientation.
      *   <li>Vertical Reachability is enabled.
+     *   <li>Activity fills parent horizontally.
      * </ul>
      */
     private boolean isVerticalReachabilityEnabled(Configuration parentConfiguration) {
@@ -753,10 +759,14 @@ final class LetterboxUiController {
                 && parentConfiguration.windowConfiguration.getWindowingMode()
                         == WINDOWING_MODE_FULLSCREEN
                 && (parentConfiguration.orientation == ORIENTATION_PORTRAIT
-                && mActivityRecord.getOrientationForReachability() == ORIENTATION_LANDSCAPE);
+                        && mActivityRecord.getOrientationForReachability() == ORIENTATION_LANDSCAPE)
+                // Check whether the activity fills the parent horizontally.
+                && parentConfiguration.windowConfiguration.getBounds().width()
+                        == mActivityRecord.getBounds().width();
     }
 
-    private boolean isVerticalReachabilityEnabled() {
+    @VisibleForTesting
+    boolean isVerticalReachabilityEnabled() {
         return isVerticalReachabilityEnabled(mActivityRecord.getParent().getConfiguration());
     }
 
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 e5ff91f1ba373..de0999f7e8981 100644
--- a/services/tests/wmtests/src/com/android/server/wm/SizeCompatTests.java
+++ b/services/tests/wmtests/src/com/android/server/wm/SizeCompatTests.java
@@ -2583,6 +2583,133 @@ public class SizeCompatTests extends WindowTestsBase {
         assertLetterboxSurfacesDrawnBetweenActivityAndParentBounds(organizer.mPrimary.getBounds());
     }
 
+    @Test
+    public void testIsHorizontalReachabilityEnabled_splitScreen_false() {
+        mAtm.mDevEnableNonResizableMultiWindow = true;
+        setUpDisplaySizeWithApp(2800, 1000);
+        mActivity.mDisplayContent.setIgnoreOrientationRequest(true /* ignoreOrientationRequest */);
+        mWm.mLetterboxConfiguration.setIsHorizontalReachabilityEnabled(true);
+        final TestSplitOrganizer organizer =
+                new TestSplitOrganizer(mAtm, mActivity.getDisplayContent());
+
+        // Unresizable portrait-only activity.
+        prepareUnresizable(mActivity, 1.1f, SCREEN_ORIENTATION_PORTRAIT);
+
+        // Move activity to split screen which takes half of the screen.
+        mTask.reparent(organizer.mPrimary, POSITION_TOP, /* moveParents= */ false , "test");
+        organizer.mPrimary.setBounds(0, 0, 1400, 1000);
+        assertEquals(WINDOWING_MODE_MULTI_WINDOW, mTask.getWindowingMode());
+        assertEquals(WINDOWING_MODE_MULTI_WINDOW, mActivity.getWindowingMode());
+
+        // Horizontal reachability is disabled because the app is in split screen.
+        assertFalse(mActivity.mLetterboxUiController.isHorizontalReachabilityEnabled());
+    }
+
+    @Test
+    public void testIsVerticalReachabilityEnabled_splitScreen_false() {
+        mAtm.mDevEnableNonResizableMultiWindow = true;
+        setUpDisplaySizeWithApp(1000, 2800);
+        mActivity.mDisplayContent.setIgnoreOrientationRequest(true /* ignoreOrientationRequest */);
+        mWm.mLetterboxConfiguration.setIsVerticalReachabilityEnabled(true);
+        final TestSplitOrganizer organizer =
+                new TestSplitOrganizer(mAtm, mActivity.getDisplayContent());
+
+        // Unresizable landscape-only activity.
+        prepareUnresizable(mActivity, 1.1f, SCREEN_ORIENTATION_LANDSCAPE);
+
+        // Move activity to split screen which takes half of the screen.
+        mTask.reparent(organizer.mPrimary, POSITION_TOP, /* moveParents= */ false , "test");
+        organizer.mPrimary.setBounds(0, 0, 1000, 1400);
+        assertEquals(WINDOWING_MODE_MULTI_WINDOW, mTask.getWindowingMode());
+        assertEquals(WINDOWING_MODE_MULTI_WINDOW, mActivity.getWindowingMode());
+
+        // Vertical reachability is disabled because the app is in split screen.
+        assertFalse(mActivity.mLetterboxUiController.isVerticalReachabilityEnabled());
+    }
+
+    @Test
+    public void testIsVerticalReachabilityEnabled_doesNotMatchParentWidth_false() {
+        setUpDisplaySizeWithApp(1000, 2800);
+        mActivity.mDisplayContent.setIgnoreOrientationRequest(true /* ignoreOrientationRequest */);
+        mWm.mLetterboxConfiguration.setIsVerticalReachabilityEnabled(true);
+
+        // Unresizable landscape-only activity.
+        prepareUnresizable(mActivity, 1.1f, SCREEN_ORIENTATION_LANDSCAPE);
+
+        // Rotate to put activity in size compat mode.
+        rotateDisplay(mActivity.mDisplayContent, ROTATION_90);
+
+        // Activity now in size compat mode.
+        assertTrue(mActivity.inSizeCompatMode());
+
+        // Vertical reachability is disabled because the app does not match parent width
+        assertNotEquals(mActivity.getBounds().width(), mActivity.mDisplayContent.getBounds()
+                .width());
+        assertFalse(mActivity.mLetterboxUiController.isVerticalReachabilityEnabled());
+    }
+
+    @Test
+    public void testIsHorizontalReachabilityEnabled_doesNotMatchParentHeight_false() {
+        setUpDisplaySizeWithApp(2800, 1000);
+        mActivity.mDisplayContent.setIgnoreOrientationRequest(true /* ignoreOrientationRequest */);
+        mWm.mLetterboxConfiguration.setIsHorizontalReachabilityEnabled(true);
+
+        // Unresizable portrait-only activity.
+        prepareUnresizable(mActivity, 1.1f, SCREEN_ORIENTATION_PORTRAIT);
+
+        // Rotate to put activity in size compat mode.
+        rotateDisplay(mActivity.mDisplayContent, ROTATION_90);
+
+        // Activity now in size compat mode.
+        assertTrue(mActivity.inSizeCompatMode());
+
+        // Horizontal reachability is disabled because the app does not match parent height
+        assertNotEquals(mActivity.getBounds().height(), mActivity.mDisplayContent.getBounds()
+                .height());
+        assertFalse(mActivity.mLetterboxUiController.isHorizontalReachabilityEnabled());
+    }
+
+    @Test
+    public void testIsHorizontalReachabilityEnabled_inSizeCompatMode_matchesParentHeight_true() {
+        setUpDisplaySizeWithApp(1800, 2200);
+        mActivity.mDisplayContent.setIgnoreOrientationRequest(true /* ignoreOrientationRequest */);
+        mWm.mLetterboxConfiguration.setIsHorizontalReachabilityEnabled(true);
+
+        // Unresizable portrait-only activity.
+        prepareUnresizable(mActivity, SCREEN_ORIENTATION_PORTRAIT);
+
+        // Rotate to put activity in size compat mode.
+        rotateDisplay(mActivity.mDisplayContent, ROTATION_90);
+
+        // Activity now in size compat mode.
+        assertTrue(mActivity.inSizeCompatMode());
+
+        // Horizontal reachability is enabled because the app matches parent height
+        assertEquals(mActivity.getBounds().height(), mActivity.mDisplayContent.getBounds()
+                .height());
+        assertTrue(mActivity.mLetterboxUiController.isHorizontalReachabilityEnabled());
+    }
+
+    @Test
+    public void testIsVerticalReachabilityEnabled_inSizeCompatMode_matchesParentWidth_true() {
+        setUpDisplaySizeWithApp(2200, 1800);
+        mActivity.mDisplayContent.setIgnoreOrientationRequest(true /* ignoreOrientationRequest */);
+        mWm.mLetterboxConfiguration.setIsVerticalReachabilityEnabled(true);
+
+        // Unresizable landscape-only activity.
+        prepareUnresizable(mActivity, SCREEN_ORIENTATION_LANDSCAPE);
+
+        // Rotate to put activity in size compat mode.
+        rotateDisplay(mActivity.mDisplayContent, ROTATION_90);
+
+        // Activity now in size compat mode.
+        assertTrue(mActivity.inSizeCompatMode());
+
+        // Vertical reachability is enabled because the app matches parent width
+        assertEquals(mActivity.getBounds().width(), mActivity.mDisplayContent.getBounds().width());
+        assertTrue(mActivity.mLetterboxUiController.isVerticalReachabilityEnabled());
+    }
+
     @Test
     public void testLetterboxDetailsForStatusBar_noLetterbox() {
         setUpDisplaySizeWithApp(2800, 1000);