Play store movie size vs Nexus 7 topic

I've just noticed an odd thing...I downloaded a movie from the play store on my Nexus 5 and it's 3.0GB (HD). The same movie, downloaded on to a Nexus 7, also as HD, is only 1.7G. What's the difference?

Granted they are the same resolution screens (right?), but if anything you'd think the larger device would have had the bigger file.