I am a firm believer in diffusion over absorption.
In my case it's "1/4/ space speaker placement in the corner between the back wall and side wall. This enhances diffusion and combines with the direct sound from my speakers and garbles up the direct pure sound of the speaker and the room.
The corner's are treated with 1" pyramid type foam panels. This dramatically improved the sound of the room cutting down multi reflections from the 1/4 space coupling corner.
My speakers are older vintage Electro Voice Sentry III studio monitors. Two per side one stacked on top of the other. The top one is upside down with the horns matting together.
Big Difference with the corner treatment. For those of you with 1/2 space coupling it may not be necessary to treat the rear wall.