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!
The ASC Matrix panel is designed for when you are close up against the rear wall. It was tested by ear and has a combination of absorption and diffusion. https://www.acousticsciences.com/products/matrix-panel
I've used the 'Live End/Dead End' concept in all my listening spaces. Nothing behind speakers and absorption panels on wall behind listening position. First reflections are the strongest and the ones that need to be addressed. Avoid overdamping!
Here is a room calculator to find where your first reflection points are and the size of absorption panels you’ll need. Just punch in your measurements in inches, feet or meters.

The treatment of a sound room is not generic. Bass issues are largely determined by the room dimensions and size. Using bass traps (real bass traps) is almost always beneficial. Moving into the mid and high frequencies, the treatment often depends on the speaker placement, type of speakers, wall covering, floor covering and furniture. Real diffusors should not be placed directly behind the listening position. The listening position should not be close to any real diffusors. How close depends on the type of diffusion and possibly room size. Minimum 5 to 6 feet. Place absorbers behind you and avoid over-damping as stated previously.

For a diffuser to work, it has to be a "certain" distance from the listener's ears. I put certain in quotes because the distance is frequency determined. A Google search will lead you to the related data, but start with the YouTube videos posted by Acoustic Fields.

Your ears being only 12" from the rear wall (or even twice that), I would say diffusion is out. Simple Owens Corning 703 panels (covered in material of your choice) is a good choice, the 703 being what almost all commercial makers of absorbers (GIK, ASC, etc.) use.