I am using diffusors from Core Audio Designs behind my speakers. The speakers, which are a front radiating cone design, are just 28" from the front wall (measured from the tweeter), due to space limitations. Adding the diffusors behind my speakers increased perceived resolution, added depth to the soundstage, made the speakers less localizable, and enlarged the image sizes.
I also experimented briefly with absorption, but in my setup, the only improvement was increased perceived resolution. Soundstage depth, speaker localizability, and image size either stayed constant or got worse. I'm not sure what the results would have been if my speakers were farther away from the front wall, but I suspect it would have been similar in kind while less in degree.
The Core Audio Designs diffusors are also among the most attractive room treatments I have seen. I have no connection to the company.
Good luck.
I also experimented briefly with absorption, but in my setup, the only improvement was increased perceived resolution. Soundstage depth, speaker localizability, and image size either stayed constant or got worse. I'm not sure what the results would have been if my speakers were farther away from the front wall, but I suspect it would have been similar in kind while less in degree.
The Core Audio Designs diffusors are also among the most attractive room treatments I have seen. I have no connection to the company.
Good luck.