Monopole speakers all around is best for Atmos. I replaced four QS8s with four on-wall M3s, lowered them to be just above seated head level, and used four more on-wall M3s mounted to my ceiling for the overheads. I have a room with a lot of soundproofing (and acoustical treatments), and there was no way that I was going to try to retro-fit 4 in-ceiling speakers, through my ceiling's double 5/8" drywall, plus GreenGlue, plus hat channel and whisper clips, with my master bedroom right above the theater room. If I was building from scratch again and could have designed back-boxes to keep things soundproofed still, I would have gone in-ceiling.
Anyway, it is really impressive when you get a well mixed movie. Be aware that many times it isn't what you hear when watching an Atmos (or DTS:X) encoded movie that you notice, but it is what you don't hear if you turn off the overheads that makes you realize how more enveloping these audio formats are.
