room size question.

bshaw

I would suggest measuring from the center of the front of the speaker for side wall and listening distance , to the back of the speaker is ok for the front wall .

Try moving the speakers so that you have 36" from the side wall to the center of the speaker and see if you like the sound ,  you really don't have much room for moving away from the front wall , have you tried moving the speakers closer to the front wall with 30" being the closest before the bass becomes boomy and don't worry about having an equilateral triangle .  

After trying all this , maybe acoustic pannels ( diffusers-diffracters , not absorbers )

on the side walls .

you may also try the distance between your speakers , be 83% of the distance between you and the speakers.

Virtual system about your room could help.

GIK Acoustic gives free advices according to your room’s measurement

I don't want to assume what you are thinking, but so far:

you tried everything with speaker placement and seating position and volumes

room is treated

it's a decent size room

it should produce a soundstage

your layers are either not produced or something "eats" them.   

you think it's your room size. I think it's synergy and I assume it's the lack of, between the speakers and the room. (and I hope this will be the lamest, most useless comment you will get today)

I sympathize with OP’s frustration here, as I have at times experienced a similar confusion about what exactly a deep soundstage should sound like and wondering why I can’t get whatever that is. I hope I am not being overly reductive or patronizing when I suggest that some part of this kind of confusion may come from not having a baseline expectation to work from - and instead imagining what is probably an unrealistic representation of a staggeringly deep, almost surreal soundstage that extends dozens of feet beyond the speakers. After all, that seems to be what many fellow audiophiles have, or at least are able to describe having. I have never heard such a thing in my own room, though - which isn’t to say it’s impossible, but that my particular room/system/setup likely precludes achieving it, which would seem reasonable considering the compromises I’ve had to make. The somewhat confusing psychology of not being able to achieve the perfect soundstage sometimes leaves my brain suspecting that I have no soundstage at all, and that what I’m hearing is just a pleasant but flat centered image. That psychology can be so powerful that it makes even a perfectly reasonable soundstage seem dull. A third party observer who came over to listen might completely disagree and think it sounds great.

I think I have just invented the theory of general relativity of soundstaging.