I’m going with M3 on walls on the ceiling as top middles and M3 bookshelves as front and rear heights.

In a small space front to back this should give you max separation. It also lends itself to be configured for ATMOS, DTS and Auro 3D (if you wire for two more speakers for front center and mid center). I wired several other locations as well just in case but they are probably a bit much if your room is too small.