Aram: There's no one set method. You have to remember every room is different. Your listening position will also have a large influence. One thing to keep in mind is don't let the sidewalls be at the same distance as the rear wall or a multiple of it.
Room treatments can also make a huge difference and are a necessity. You don't mention them but if you have some what are they?
At minimum all first reflection points should be treated and at least two bass traps are necessary. More treatment helps alot, it's similar to buying better speakers.
What I've said goes for all speakers. Once you get that done then you can adjust the RM/x's to your liking further.
