It seems counterintuitive that a dip in a frequency band can be replenished by absorbing more of that and nearby ranges, but it is exactly what gets you back to better sound.
New room, new gear, set-up first reflections and speaker placements mathematically. Then ran room sweeps and anguished over the room modes I hoped were not going to develop. I played with some 2 inch spare panels stacked up 8 or more inches thick behind the mains to see the effect and those sweeps said it would work.
Ultimately, I built rear corner tri-traps from Roxul, and made massive front traps from 703, Roxul, air gaps, and plastic sheet (ala FRK) for more targeted effect. These are about 24 x 32 with large Real Traps Mondo traps in front and GIK art panels in front of those. So more like 38 inches deep. I put the plastic on the inside surface and then put a cloth panel over those.
This is NOT the look I was going for. Oh well.
For brevity, the combined and generous 1/3 resolution graphs of the before and after show the improvement. Down to a decent +_ 4db deviation. Not the prettiest result, but now I actually have deep bass coming out of the Wilsons.
https://www.audiogon.com/systems/10635