Absorption, Diffusion or a combination of it all?

Taking time to research. I’m using the panels that I already have to experiment. I’ll play with REW soon. We’ll see what it does. 

@kota1 -- thanks for the video--i only watched starting at :49 but it seemed to me the discussion was more pertinent to home theater setup (which you have) rather than 2 channel setup (or 2.1).  Can't help but wonder if his "formula" is based on having center and side/back surround speakers in the mix and thus maybe overdone?

As for diffusion v absorption behind speakers as w anything it depends--in my room i have a large window behind my speakers and, therefore, opted for absorption (of high/mids) behind the speakers with a curtain rod and heavy drape and it worked well.  When i slide the drape out of the way and play with the the wood venetian blinds of the window (as a diffuser of sorts?) it produces an interesting effect that is not displeasing but seems to de-focus the soundstage.  

Someone above said smaller rooms have different challenges than those addressed in the video and are more challenging. I fall into the wolf garcia crowd of just doing a few things (bass trapping), first reflection and aforementioned absorption and then just enjoy the music (although admittedly i measured frequency response in every part of my room first, mainly for speaker placement and knowing where the bass was emphasized--which, surprise, the usual corners)--i only spent three or four hours total and I'm happy.  As someone else said above, unless your room is really problematic don't obsess over treatment tweaking.

@wyoboy 

The setup is the same for both 2 channel and HT, Look at the room kits at is website and you can compare both setups. I have a large windo to the right side of my MLP and I hung a diffusor called an acoustic lens which allows the light to pass through. You can see a pic in my profile system. You will see that the room kits are determined by the size of your room

Here is the layout for 2 channel (they also have HT):

https://www.sonitususa.com/product/studio-acoustical-systems

@kota1  I'll check out their site-thanks.  Interesting that acoustic lens over the window--is that the squarish thing that seems to be hung over vertical blinds?  If so, can't help but wonder if the verticals all by themselves could have acted as an "acoustic lens" similar to the way i played with the blinds on the window behind my speakers.  Have you ever removed it and heard the difference ? 

Although i only spent a few hours on room treatments i will admit that i started down the rabbit hole by reading Jim Smith's book,  "Get Better Sound" and then booked an hourlong phone session with him b/c i had several questions on material in the book as well as idiosyncrasies in my room with doors--he was quite helpful but also urged me not to obsess beyond dealing with a few important things pertaining to my room.

@wyoboy

Yes, the acoustic lens is the squarish thing. I had the vertical blinds long before I had the acoustic lens diffusor, they don’t do anything. I got the idea to hang it from a recording studio that had the same issue and had the acoustic lens hanging and it did the trick. You'll see in the pics I also have a "cloud" of acoustic lens hanging at the rear of the room below my PJ. All I did was follow Anthony Grimani's acoustic recipe. Here is a link to the various diffusors I use in my setup:

https://www.oeler.com/pdfs/Sustain-Data-Sheet.pdf