I also feel like music is using a lot more dynamic objects that can utilize 4 top speakers than movies do (probably depends on the genre as well).I never tested myself but the test I found on youtube from a reliable installer mostly detected 7.1.2 coded into movies. Which makes probably sense for big audiences so everybody get's the same ceiling information?
For music 7.1.4 seems more standard.
And as you said, 7.1.2 might make more sense for a movie setup because you don't get interference between the front and rear top row of speakers which would play the same signal.
The ultimate best setup should be 7.1.6 because though if the budget and rooms allows for it:
The .2 of the 7.1.2 bed layer will still play through only 2 top speakers (those directly above) while the other 4 atmos speakers will be used if there are dynamic objects flying around
-You won't get interference and this phantom image between speakers playing the same signal but you still have enough top speakers for that 3D height effect with dynamic objects.