Atmos in ceiling speaker setul

Does your receiver have options for front/middle/back height channels?  Take a look at the dolby website they have every possible configuration with layouts. I personally have 4 ceiling speakers (middle/back) and works well.  You could mount your height speakers a bit lower to get correct angle - may work for your space.  

how did you convince yourself that height speakers were desireable?

In any case, I would never compromise the main 5.1 setup for additional surround effect.

btw, do you have 5.1 now, anywhere?

what content, 5.1 or 7.1 do you have/stream? my receiver, or cable company make pseudo surround quite often, I make it a habit of changing to ’Direct’, and very often the sound improves, often 2 channel stereo sounding easily superior to ....

this is a reason to have your mains large enough to make good full range sound (enough bass so you don’t think it’s missing), rather than relying on the sub for your bass all the time. In my home theater, the sub is to extend the full range main's bass, i.e. Jurassic Park Dinosaur Stomp.

IOW, If it’s not real or pseudo 5.1, then there is no .1 sub signal to the sub. If 2 channel sounds better, no bass sent to/produced by sub.