I don't see Atmos having serious consideration unless the OP can wrap his head around all the really good reasons there are,
to limit the space to a single row of seats. Then I prefer ATMOS 5.1.4 with dual smaller subs, for such a space. The price of giving
up the second row, is the loss of seating. The upside audio-wise is substantial. Instead of six audio compromised seats, you can have
an optimal seat and all three seats can be off of every speaker. You also gain substantial creature comfort, and have some semblence
of space. I'd even recommend seating on the narrow side of things, to help gain a few extra inches of side wall separation.
The biggest lessons I have learned from dealing with a smallish space over two decades and many rebuilds, is one can have a pretty solid
room, but one is constantly editing and there's a real need to constantly rein one's self in. You can have some special features, but
you need to be choosey and disiplined.
5.1 has solid merit simply because you can raise a pair of dipole surrounds up high. And get at least some seating/surround
speaker separation. I would suggest one go sit a foot away to a surround speaker and see how that spoils the surround magic
for you. And then consider how one is to set the surround speaker levels, so that speaker isn't drawn out of the surround mix.
And yet can be heard several seats over.
Raising surround speakers, for any ATMOS layout, isn't a solid option.
Some seating "wiggle space" might also be a blessing to have with a single row, to have an option to move the seating 6-8".
That might just be a really easy tool to avoid a nodal issue and gain smoother audio.