Couple of things. One, taming a very live room by controlling mid and treble reflections makes the bass stand out more prominently, so this could just be mid/treble absorption. Another thing that happens is that valleys are reduced... if you had set the bass level based on the "average" bass level then that just came up a great deal.
Usually we find the opposite is true though, usually some exaggerated room mode has so much output we have to reduce the subwoofer level, and then find when we've clipped those peaks we can now bring the sub level up and it sounds much more full and complete.