Thank you!

I actually made a sketch of my room for the GIK acoustician. I'll attach it to this post.

After a lot of thinking, I've decided to actually turn my setup 90°, so I'm no longer facing the longer side of the room. I didn't want to do that before, because I didn't want to block the windows, but at this point I no longer care about that.

I've also proposed this to the person at GIK who is helping me. If he says this is a good idea, I'll definitely do it.
I'll measure the room with REW again then of course, and I'll make sure to not sweep too loud then.

If anyone here has more input in the meantime: please go for it.