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.