In my 15' wide room, speakers on the short wall, I tried Gik Polyfuser absorber/diffusers, then 2' x 4' 244 bass traps with scatter plate, and finally, three 2' x 2' 2A Alpha absorber/diffusers at the first reflection points for my speakers. A vertical row of 2' x 2' Alpha absorber/diffusers sounded the best to both myself and my wife.
I also have Gik's Tri-traps in the upper room corners, 244 bass traps behind the speakers, and the Polyfusers mounted in back of the row of Alpha absorbers. A large double pane glass patio door with heavy curtains is on the wall in back of the speakers.
I'm sure Gik will give you specific advice for your room if you ask.