My room is roughly 9m x 5m x 2m and I happily went from 7.1 down to 5.1. The sides were too close not to be localisable and thus distracting.

Main System: Trinnov Altitude 32-8-16, 271, 2 x 8KXE, 1 x 8KPP, 6 x M6 Surrounds, Rel No.25, Oppo 203, Zappiti Pro 4K HDR, Roon, WiiM Mini.