diffusion at first reflective points + what ive learned about room treatments

(a bit of a "sin", perhaps, but just can't tackle using REW, so, I'm left to "trial and error")

Sharing an, albeit long, observation that for my listening room diffusion at first reflection points (so far) sounds quite a bit better than GIK four inch thick, 2 foot by 4 foot absorption panels mounted two feet high off the floor, flat against the side walls at first reflection.  I had been using this set up for the past year or so. 

Room is 13 feet wide with 11 foot long side walls and NO REAR WALL and 9 to 11 foot high cascading ceiling in a loft setting.  Spks are Harbeth 40.2 40th anniversary models 3 feet out from the front wall to the speaker backs and only about 2 1/2 feet from the sides of the speaker to the side walls.  Listening position is 8 feet, 3 inches from the speaker plain. Speakers are about 8 feet apart tweeter to tweeter.

Did tons of research and actually got advice from Fidelis, distributor for Harbeths in the U.S., that diffusion at first reflection points works very well. I decided to actually order more "room treatments" after trying said panels and another set of four foot tall, 6 inch deep, corner bass traps around the room to find they did not "work" on the front wall behind the speakers in corners or where ever (less dynamic, open sound) but could still detect slap reverb in the room. Didnt really like the sound of absorption panels on side walls either but they were taming "brightness" at higher volumes. (Thin cotton bedspread on the ceiling helped a lot)  Discovered opinions that parallel walls are the most in need of treatments and found this to be true with a set of 2 foot by 4 foot slat panels behind the speakers but on the side walls. Was surprised the sound was more "open" and "alive" but not brighter despite no rear wall reflections and the panels were on the sides behind the spks.

Replaced the GIK panels at first reflections with the ATS 6 and a half inch deep diffuser panels that are plywood and rather heavy.  Have read many times that diffusers need to be at least 6 inches deep and a good distance away from the listener to work properly.  My ears are a lil over 8 feet from the center of these diffusers and the sound is way more 3D, cleaner, better blended and gives the impression of a larger, wider and higher sound stage. Speakers "disappear" better.  I may have noticed that certain midrange features that used to jump out blend with the overall presentation a lil more. Bright recordings somehow still sound better with the diffusers and less absorption.    Using acoustimac 6 inch bass traps at second reflection points at the very end of the side walls closest to the seating position for now.   Each are topped with 2 foot by 2 foot smaller, thinner wood diffusers that seem to ad a lil more perception of space.   Certainly not done here. Thinking of skyline diffusers for the ceiling first reflections. (vicoustic comes to mind)

I thought I'd share my experience that seems to run a lil counter to the audiophile "rule" of addressing first reflections with absorption.

This latest audio journey followed my question a while back here on the Gon about thin, bright sound that brought many responses about room treatments that were correct.  Only thing is I found a lot less absorption was the ticket for the loft. (again no rear wall)   It all diverged into equipment upgrades ala speakers, dac, preamp. vibration control, lots of room treatments, etc. So, I feel a debt of gratitude to the responders to my initial question. (wallet not so much)

Thanks very much!!!