Does direction of the sound determine what kind of diffusor?

[pepar]

I have read some threads here and on some other forums and understand the basic .. basics. But when and where to use what still eludes me. For example, the sound strikes my back wall initially dead on. My rear seats are about 7' from the wall and right now I have 2" OC SelectSound Black panels there sized to be for the first reflection points for LCR and all seats. (BTW, when I added my FRP absorbers, the rear one made the most difference.) If I were to replace the absorbers with diffusors, what type diffusor whould be best.

Also, I am looking at reducing the vertical dimension of the front L&R FRP absorbers. Since my LCRs have been relocated to be very close to the plane of the listeners, I do not need as tall a panel. And I am considering installing diffusors above and below the newly sized absorbers. The initial sound strikes that from an angle, and most of it (from the speaker closest) strikes it at a shallow angle. What would be the best type of diffusor to use there? For these, I would prefer that as little as possible is scattered back to my (completely dead) front wall.