Yeah, my current space is 24 feet deep for physical room, remove about 3 feet or a hair more for the false front screen wall. My rear seats are about 2.5 feet from the rear wall.

The biggest thing to keep in mind for Atmos is getting a good amount of separation between your "bed layer" speakers (5.1 or 7.1 speaker configuration) from the overheads (#.#.2, #.#.4, etc)

Get your bed layer right, and you will get a bit more flexibility in your overhead placements.
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2-M60s, VP180, 8-M3s, SVS 20-39PCi, DIY Sub, 8-Shakers, JVC RS45, Anthem MRX-1120