Spacing Diffusor Panels

How important is it to have all your diffuser panels adjacent to each other?  If you’re placing diffusion behind your speakers and the wall is 20ft wide how important is it to have No Gaps between panels? If the panels are 3ft wide and you’re using three should they be arranged adjacent to each other thereby creating a continuous nine foot wide diffusion area or can they be separated by two feet or more? Does a non continuous alignment adversely impact the diffusion?

First question.  Are these QRD (Quadratic Residue Diffuser) diffusors?  If so, then the placement and direction will definitely affect acoustics in different ways.  When I say "direction" I mean the placement of where the shallow slots are vs. the deep slots - also vertical or horizontal.  It the room is huge, such as 20 feet by 20 feet, then it may not matter much (unless the diffusors are placed in the corners).

There is no hard and fast rule on placement.  I would probably say that you should not place the close to or behind the speakers because they can actually cause phasing problems with certain frequencies the speakers are producing.  They can be placed together or you can split them apart by a couple of feet.  Do you have the ability to temporarily mount them and listen to the result?  This may be an exercise in experimentation before you decide on the best result.  It was certainly this way for me when I added QRD diffusors to my room.

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

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.
that brings up an interesting question; what 'sound' actually comes out of the back side of Magnepan's?  Is it an Exact duplicate of the sound waves that are emitted from the front?

If the sound from the back of the Maggies is 'not good' then why would you want it reflecting off of the front wall back into the sound field?

But, more listening is required.  My initial impressions are that in general the sound is better overall and that the room just seems more natural sounding with the diffusors on the front wall.