If you go heights like this:

https://www.dolby.com/siteassets/ab...s-setup/4_1_2_overhead_speaker_setup.pdf

Since you are MLP focused (no center channel) you can cheat the ceiling speakers closer together and ahead a bit. I wouldnt go for wall corner heights. As rrlev said best practice is seperation between bed and heights to get the best bubble effect.

Only way it works is if you go something like beds, heights and tops. But that is not supported strickly speaking by any single format.

If you put your M5OW on T-brackets on walls for surrounds and QS10s on ceiling that would be pretty badass.