I am not mounting these flat on the ceiling. They are being mounted using the full metal bracket that Axiom offers for mounting speakers to the ceiling. I had Axiom pre-drill the mounting point into the back of the M5HP on-wall speakers and they replaced the speaker connections with standard speaker connections. They assured me that the M5HP would be fine with the FMB as they do not exceed the weight tolerance of the brackets, as long as they are mounted into a ceiling joist/stud, which I most assuredly will do.
This approach is similar to what other Axiom members have done for Atmos ceiling speakers. I believe nickbuol is using M3 speakers. I was originally considering the M3 but then decided to do all M5HP speakers for all suround/Atmos speakers. After speaking with Axiom, I'm confident they will work. And personal experiences shared on this forum suggest full-range speakers are suitable, and preferred, for Atmos ceiling speakers.
I don't disagree - these are likely overkill. But I purchased them at their initial price and I thought, what the hell, go big or go home
We'll see if they work out.
I'm preparing to hang them now. Just determining final locations once I get a stud finder that confidently confirms the joist/stud locations