When playing a movie/show on the Apple TV and the information is relayed to the iPhone Lock Screen controls, the image displayed is the background art. The metadata image is a wide rectangle which then gets resized into a square and ends up relaying very little information at all. In contrast, the Plex Apple TV app displays the poster art which actually fits in the available space.
Infuse
Plex
Is this a planned improvement for the 7.0 release that is said to include some UI revamps?