Absorb or Diffuse Behind Listening Position?

Hey All. Starting to finally treat my listening room. My listening position is up against the rear wall (head probably being spaced about 12" from the wall when sitting down). I’m putting 2’x4’x2" absorbing panels behind the speakers, but what should I choose for behind the listening position? Diffusion or absorption?

There are al lot of windows in the room, with horizontal louvered shades which act as pretty decent diffusion; and a big built-in bookshelf on one side wall also helping with diffusion. On either side of the wall behind the listening position are a pair of glass French doors, untreated at this point, and the room sounds a lot better when they are left open to the big room on the other side of the wall. I haven’t tackled the ceiling yet either. Thanks!