The good thing about having speakers in corners is that you know the sound eminates from the corner apex and is limited to the 90º wall angle, consistently for each speaker. But with four speakers in a relatively small room, it might be good to shift the bass bins forward or inward a bit from the rear wall, to average the sound field and possibly fill in a null that might have otherwise formed. So take a minute to look at the references below, and you may want to spend some time and do an analysis of your room. That way you'll know if you want four identical seven π speakers in each corner, or if you'll want to move bass bin of the rear pair forward or something.