Diffusion vs. Sound Absorption views

I am keen to check out this diffusion aspect of sound treatments, as I have a remarkably dampened room (two layers of 5/8" sheetrock with Green Glue in between and several sound panels behind the speakers, and thick carpet in the room.)   I have a long narrow room (13x26x9) with the speakers on the long wall, about 3' from the wall, and I sit about 10' away on a sofa against the rear wall.  Not an ideal setup for sure, but I am working around the edges with what I have.  
If diffusion enhances the spatiality of the sound, then I am interested to explore this aspect of my system.

I listen to about 98% jazz, of the straight-ahead variety.  Miles, Coltrane, MJQ, Brubeck, Desmond and most significantly Stan Getz. 

Since you have Spatials, why not contact Clayton Shaw, owner,
and ask the source. He is a person very willing to share. Overall
I understand absorption be best used to stop early reflections,
ie in front of speakers on side walls and ceiling. Diffusion best on front and back walls.

Essentially 
Diffusion everywhere, particularly front and back walls and ceiling in your case. 
Absorption only where benefits are obvious through experimentation 

How do you know when panels are needed? I'm interested in the topic, but don't notice a problem with Golden Ear Triton 3+ about a foot from front wall and 6" from side walls. If it already sounds good don't mess with it? Tinker for better sound? Or is there some measuring equipment for this? 

Conventionally, diffusion improves perceived ambiance while absorption improves imaging.


I suspect that the answer is somewhat dependent on the distance from the rear of the OB loudspeaker to the rear wall.  Why, if the speaker is too close, then there is much more of a chance of the out of phase wave interfering with the sound coming off the front...so absorption should help.Here is a brief but interesting article:

http://www.gikacoustics.com/speaker-boundary-interference-response-sbir/


I think that you can "simulate" the effect of diffusion by moving the panels out from the wall another 2-3' (not that you are going to leave them that way) which will then give you a different combination of direct sound, reflected sound and absorbed sound.