Hey Mike,i had a double height RPG Skyline diffuser center middle on the wall behind my speakers for a number of years. i put it there to clean up the center image....a net gain i thought. but once i tamed some reflections here and there, i needed to check to see if the Skyline was still helping. so i covered it in plastic sheeting.....better. then i completely removed it. much better. it had been a band aid reducing excess reflections, but once i got those under control it was deadening the music energy and confusing the music focus.
i had window inserts built in 2011 but could not hear the difference in or out, i liked the view, so kept them out. 4 years later in 2015 as i cleaned up reflective glare i brought the window inserts out of storage and tried them again, now they competed and filled in my sound staging and added coherence.
my sidewalls along side and behind my speakers were bare. but as i tuned things that was one area i could not quite figure out. i tried a number of things. it either was too much hash, or too dead. finally i tried some Aural T-Fusor diffusers. perfect. i had not understood the problem; my 36 inch long, 7 foot tall bass towers near that wall had a resonance going on between the wall and speaker cabinet that higher SPL's excited. the T-Furors quieted it. this is something i would never have figured out if i did not methodically chase the fine tuning process. you open a door, and then see another wall in front of you. then find the door.....open it, and see another wall. until no more walls.
as you fine tune things previous perceptions must again be checked and proven and keep your mind open.
Sounds like you’re as nerdy as I am… although very meticulous - I like that, and was laughing so much as I saw myself in your story… LOL!!
/ Jk