I have a 20' x 15' home theater. My only treatments are a thick almost shag dark rug; a piece of that rug on the back wall to minimize slap back, and dark grey walls and ceiling to minimize light reflections. I should put something on the ceiling and certain walls since I can hear sound reflection depending on volumn, but prefer not for aesthetic reasons. I can't have the wall corners attenuated due to my dual array speakers. It would defeat their purpose of providing a deep sound stage.
FYI, I got tired of front directional speakers years ago. Looking for that elusive stage depth I tried Bose (not impressed), went to Ohm's (too short), Mirage towers , and finally Def Tech because of their powered sub-woofers and a more neutral tone. I now use the Mirage towers for the rear surround and although I could initially hear the tonal difference between them and the Def Techs, I don't notice it anymore. Anyone who has heard my setup are stunned by the realism. Don't need no stinking 7.1 or more.
Make a “cloud” for the ceiling. You can build one in such a way for it to be pleasing to the eye. Here’s what I discovered while figuring out how to treat my studio: If you can hear reflections, that’s very bad because they’re obviously muddying up what’s coming out of your speakers, but at least they’re obvious. But the other stuff, standing waves, dropouts and exaggerations are just as bad. Trust me - after building and then installing corner bass traps my room, which already sounded pretty good, sounds amazing. The soundstage opened up, I could hear every bass note without “boominess” and clarity and coherence improved. The proof was that mixdowns translated great - car stereo, boombox, earbuds etc. My mixes now sound great on everything without having to constantly tweak this and that to get them sounding good on all playback devices. A quick tip: If you do install corner traps, try to allow a space between the trap and the wall. Essentially doubles effectiveness. But trust me - it’s the stuff you can’t hear that’ll mess up clarity more than the reflections you can hear. After you deal with that, your jaw will hit the floor.