Acoustic question

The ceiling is a highly under appreciated location for treatment, but for the side I want you to consider diffusors, especially close to the speakers

You are on the right track, try some changes with the room divider and maybe some absorbers and see how that goes. I have a dedicated listening room but it's still a room and not a laboratory, I get great sound with just a few tricks. 

I have a very similar room. I would not use absorption on the long side wall. I used diffusion and it works wonderfully. I also found I had to pull the right speaker about .5 inches closer.

Absorption is always my distant second. I find diffusion, in general,  works far better. I have used absorption in the past with a dulling effect I did not like. Even a little of it had negative unintended consequences.

Diffusion on the front and long side wall worked for me.

@grannyring,

 “I also found I had to pull the right speaker about .5 inches closer.”

 Closer to what?

To you. If you draw a line across the front plane of your speakers you may find moving that right speaker forward a half inch or so will improve center image and dial in the sound. Small increments for as little as 1/8 of an inch make a difference.

In room set ups that are not perfectly symmetrical this sort of dialing in position really helps.