Dolby Atmos doesn't have a spec for 2 sets of height channels. They prefer in-ceiling, bouncy-house, or a mix of both for x.x.4 speakers.
But there
are specs for x.x.6 where 4 are heights and 2 are tops:
View attachment 61939
And the
only x.x.8 channel mode listed has 2 sets of heights and 2 sets of tops:
View attachment 61940
At this point, I'll mount my speakers high and let there be a phantom top. It's possible, just not ideal, but still better than bouncy-house. Gotta make things work for the room you've got.
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But... I just bought another set of the same height speakers which I'll try to mount on the ceiling.
In my room, the biggest issue is getting wires through there. I have 4 can lights near where I'd want my speakers. I could use those holes to fish stuff through, but my dad (who helps me with this stuff) isn't keen on touching anything in the ceiling right now.
I can always mount them on the ceiling and run visible wires, but my wife will probably complain. The only other way to get top-mounted speakers is going through the 2nd floor floorboard which requires pulling up the carpet and running wires through those joists.