Bass actually is omni directional to the degree that low frequencies sort of crawl along surfaces and react to room corners, etc. If you walk around the room as Dudley suggests you understand this fact, not negate it. I have one sub right behind my left speaker, and another smaller sub a couple of feet away from my right speaker against a wall where I can easily put it in the window to service my deck sound needs when appropriate. The second sub sort of tempers the other one to smooth out the whole thing ("swarm" sub systems do that well I've heard). I actually would try Dudley's method if REL decided to offer their "Longbow" wireless system in a version that could be used with older models…I mean it's simply transmitting to something in the High Level input at the sub…come on REL! This aside, my 2 subs sound great as is.
Move your sub
Caught an Art Dudley video about moving your sub(s) from behind, beside or between your speakers to the seat end of the room. I moved my REL back so they are in the same plane as the listening position. Much better! Try it.