Spacing Diffusor Panels

I agree, you don’t want diffusion too close to your seating position  or speakers because comb filtering can become an issue.  From what little I understand that effect is partially dependent upon the effective frequency range of the diffusion panels which is determined by their well depth.  The diffuser I’m using is a simple one-dimensional DIY design (they’re called HomeDepot Diffusors 
https://www.google.com/search?rlz=1C9BKJA_enUS796US796&hl=en-US&ei=5atMW-

They are hanging on the front wall approximately 6.5 - 7 feet from my Magnepan’s.  Actually they are sitting directly on the floor at this point, I haven’t gotten around to mounting them on the wall yet.  

yeah, these look like a variation on the QRD type diffusors.  You can cut some 2x4s and just put them under the diffusors to raise them up - or use something else to place them on so that you can hear them up high. 

Since the sound from the back of the panels will not be particularly good, why would you want to diffuse it, thereby adding an unnatural sound to the room acoustics? 

Personally, I would prefer to absorb that back wave.  Reflecting it any manner cannot help, IMO.

It’s my understanding that the sound coming out of the Maggie panels, front and back is exactly the same; only they are in opposite phase.

i’ve tried Absorption and did not like the result; just deadens everything especially the top end.

The diffusors do expand the sound field behind the panels and I like that effect.  Balance is the key; not too much diffusion and not too little.

Very careful placement of the absorption panels is required, as well as using the correct size.  Too much absorption can definitely kill the sound's liveliness.

Re the sound from the rear - it's not even close to the sound from the front.  If for no other reason, think of how you have the panels configured.  That is backwards - or at least very different - from what you chose for the best sound from your seat. 

Maybe it's close to the same sound if the speakers are pointed straight ahead, but who does that?  Multiple panels per channel (Tympanis, 30.7) can be worse as the the time and phase differences are reversed.

When I worked at Magnepan as Natl. Sales Mgr., ( I wrote the set-up manuals for T-1D, MG-1 & MG-2A), I can guarantee you that we did not want to disperse the highly colored reflected sound. Doesn't mean that in some cases/installations it might not be preferred, however.