VR Viewport shrunk toward bottom of screen on iPhoneX

I have a VR Cardboard app made with Unity 5.5.1 and Google VR SDK 1.3. The build works perfectly on Android, iPad Pro and iPhone 6 but the viewport breaks on iPhone X: https://i.stack.imgur.com/hBpM1.jpg Viewport shrunk & cropped to a small box at the bottom of the screen iPad: https://i.stack.imgur.com/FWhRm.jpg Larger viewport, with margins at the top and sides Is there some iPhone X specific provision that needs to be made or is it just a bug for this model in this Unity version?