If you are forced to put your speakers closer to the rear wall than necessary, you may want to consider reducing the relfections by padding the wall directly behind the speaker. If the wall behind your speaker are glass windows or French windows, you may want to invest in heavy drapes. This has a got an added benefit for home theater fans since it keeps the room nice and dark. Control side wall reflection also by putting a bit of furniture etc. If you have a perfectly square room, you are really going to suffer.
Circular rooms are also weird.
If you are having a serious bass boom, try throwing a carpet in between the speakers and your listening position. This can work wonders if you have a concrete floor.