Geoff,
If you want to be sure whether it is related to position, I'd recommend you get an SPL meter and run some sound signal sweeps. It could be that your listening position sits in a null for bass response. One good way to figure this out once you have an SPL meter is to use the free Room Equalization Wizard software (a google search will turn up a tutorial on the Home Theater Shack forums). It takes a bit of work to become familiar with it, but once you understand it, it is an incredibly valuable (and free!) tool.
This will show you if you're getting subpar bass response across the frequency range, or if you're experiencing nulls in common frequencies that may give make the bass less than you want it to be. In my room when I first set up the EP600, I was really disappointed, but after reading recommendations here, I ran the REW software and found that I had an enormous dip in volume at 60hz, which is where the bass was supposed to be for a lot of the music I listen to. (you can see a lot of these response curves if you go to the link in my signature) I repositioned the sub and also ended up using an equalizer to counteract my room's bass-numbing effects and now couldn't be happier. Your mileage may vary, but for me, it turned out to be a lot about position and room dynamics.
It's unquestionably more work to run through this experimentation, but it is a semi-definitive way to determine whether the problem is positional or just a matter of insufficient bass for your room.
Jason
