Tailoring tweeter output

I understand it's an old recording engineer's trick to drape a piece of toilet paper over the tweeter to tame the high frequencies. I've tried this on a few shrill recordings, and it works pretty well. It does, though, tend to reduce not just the highs in the brightness region but also in the region above that, which adds "air" to the sound. You might give it a try. It's almost free and it's easily reversible.

If your speakers are bi-wirable, you could also insert a resistor between the bass and treble inputs.
-Bob

How far apart are the speakers?

It doesn't make sense that you can move your system from the short wall to the long wall with the same results. The long wall should give you more options for speaker placement and the ability to increase off axis listening angles.
The fact that the bass was a problem on the long wall was most likely midbass which is easily cured with Tube Trap products along with Tube Trap products for the wall behind the listening position.
I know there are other room treatment products on the market, but it is my opinion ASC makes the best room treatment.
I see you have analized your room to death, but there is nothing like trial and error.
Sometimes we have to take two steps back because we went too far. Room treatment and cables alone are extremely powerful.
This is all a delicate balance and sometimes when we think we need less of one thing we actually need more of something else.

Many thanks to everyone. I will update this as I try the suggested solutions in the future.

I have very rudimentary understanding of room acoustics so I have done mostly trial and error. The long wall setup resulted in a 12-15db peak at 40Hz which is insurmountable to most traps. I even plugged all the ports and treated the back and front wall.

Most of the time, less toe in should reduce high freq energy. My problem is that the midrange driver has a narrower dispersion than the ribbon tweeter.

I think the ASC is great in offering diffusion in combination with bass trapping.

Good luck.

And don't forget to try the toilet paper!

-Bob