Coral posted shots from an event last year: Sync 4A screensIt is probably more about the app designers than the screen size. Without getting into math or grabbing a ruler which I don't have time to do right now, they can probably fit almost the same size image on the vertical screen if they would do so and overlay all of the menu items, etc. I don't have experience with either screen yet, but from the two pictures you post this is nothing about screen size but application programming and very poor choice of what they leave on the screen while using the backup camera. Blow the video image up and over lay the screen width and they'll have it made.
That post has one with the camera on the 15.5. I know eyeballing isn't easy with the different images but in the 12" screen the camera takes up the entire screen (from my own experience in the pro).