the back right corner (well, left in the picutre) where you can see a bass trap on the floor - that is very well bass trapped. as in, there's a 4inch basstrap there in a frame, then about 6 inches of dense fiberglass behind it.
but the back wall itself... unfortunately there's absolutely f-all i can do about it. i can't move that shelf or ask for anything to change there really. i guess it doesn't make a really great diffusor then, eh?
i think the solution might have to be - get a full time day job, move out of where i'm living and get somewhere bigger/of my own...
cheers mate