Confused, I'm likewise, because the bass below about 100hz is essentially non-directional and it shouldn't make the slightest difference whether you're facing the sub or have your back to it. The best corner for the sub is generally the "tightest" one, i.e. the one farther from a doorway or other opening. Also, the bass shouldn't be obvious as a separate element, it should give the impression that your mains are suddenly putting out more bass. I wonder if, as sushi may have implied, you're simply expecting too high a level of bass and if the level where it's "all but gone" isn't in fact a normal level.
