[xDrive50i]

As far as I know, the split screen is not re-sizable most likely because some split screen content (smaller or larger than the default) would interfere with the screen setup of the main screen. For example, the night vision camera fits nicely into the main screen and you can have the navigation map on the split screen. The night vision camera fills the main area exactly. If you were to re-size the split screen, the night vision camera would also have to be re-sized or a portion would have to be covered up (if larger than the default) or there would be a gap between the split screen and main screen (if smaller than default). I understand your desire to be able to re-size these screens, however I can also understand the flip side from the designers point of view where it would make things a LOT more complicated not to mention that if someone was to mess up the screens by reducing the split screen to something really small by accident, the service departments would also get swamped with unnecessary service calls... So I guess BMW decided to do a compromise and fix the split size.