If you have a screen wall that is acoustically transparent you can benefit by putting acoustic treatment tools back there that will not change the look of your room.
I can vaguely remember how you built your front wall now I think of it. Is there stone wrapped panels on each side for your VP150 L\R On wall speakers and a couple boxes in the center housing a VP160 and an in-wall Subwoofer kit behind stretched fabric?
Really, to make the most of a QRD diffuser, you want no obstructions between the loudspeaker and the diffuser.
In my experience, diffusers are an excellent choice at the front center and rear of the room. WRT to my center speaker, it made the speaker sound less like a box point source and improved perceived clarity. It also added an embellishment of perceived width of the sources, due to the vertical orientation of the QRD wells. No more balls of sound. Really, if I had to describe the benefit it would be to make the speaker sound less like a typical speaker. Voices do not sound like they are coming from a box "right there".
Diffusion can reduce direct reflections and room decay times without reducing sound energy in the room. In short, the room sound energy is of shorter duration and reflections\diffraction from the speaker's rear are shifted in phase (time)and angle. The reflections are now less detrimental when recombined with the speaker's direct sound compared with a bare reflection in our brain.
Diffusers can also be more efficient in that they do not attenuate sound like absorption while maintaining similar benefits. This is useful in large rooms or if you don't want to reduce your amplifier headroom to reach in room SPL targets after absorption. QRD diffusers are very effective and have become popular because they are easy to model and build.
Cheers.
Info.
https://en.wikipedia.org/wiki/Diffusion_(acoustics)
Buy One.
https://www.gikacoustics.com/product/gik-acoustics-q7d-diffusor/Build your own.
https://www.subwoofer-builder.com/qrdude.htm
