Hope I didn't miss it in this thread, but I don't see what the recommended minimum spacing from the wall is for the three rear ports to work properly. Any information?
The minimum distance required from the back of the VP180 or M80 or any other Axiom rear ported speaker model to let the port breath is only 2 inches.
Putting any speaker close to a wall, and even more so close to a corner, will give you quite a boost in the upper bass region. It does not matter if the ports are in the front or the back or if there are no ports at all. It is one of those things you just have to try and if you seem to have an overpowering and muddy bass then you need to move the speakers away from the wall a bit.