Absorption behind components and speakers rationale?

@emergingsoul - The reason the front wall can/should be treated is because most rooms reverberate when charged by the speakers and because it, too a different points has standing waves and reflections that will smear the sound field. 

If your speakers are ported to the rear, bottom, or sides, it will charge the front wall. Some speakers have multiple ports, some lower for the bass, some higher for the mids and tweets, so you may see a lower level of absorption and a higher level of diffusion behind the speakers, or between the speakers in the center. In my reference setup,

I’ve found Vicoustic Multifusors to be incredible in adding depth to the soundstage and making the center image as coherent as possible. I also use GIK Monster Bass Traps behind my speakers below 36”, as well as ASC Tube Traps from floor to ceiling in the front corners to absorb bass while diffusing higher frequencies. 
 

I have a pic of these treatments on my virtual system page:

https://www.audiogon.com/systems/11410

The GIK Tri Traps that are triangular are somewhat effective, but nowhere near as effective as the full sized corner traps or the ASC Tube Traps (which are even more effective). With the tube traps, you are supposed to place them with a little room between the corners and the traps so that it can absorb upon the reflection of the corner, while the front half of the traps have a diffusion layer so that it doesn’t overly deaden the high frequencies. In all fairness, the Tri Traps can now be purchased with attractive diffusion panels in front, but the Tube Traps are much, much more effective. I speak from personal experience having had both and not being a dealer for either.