It sounds to me it is more your perception of what is actually going on. Odds are the way your settings are, you are getting your max output at a lower volume. Then when you roll up your volume the mids/highs increase in volume but the sub level does not. This would give you the feeling that it is "vanishing".The enclosure is nowhere near deep enough to fill my trunk and block the opening, however it is as tall as the opening and almost as wide.
This happens to all of us and is one of the biggest reasons for upgrades. I was getting this way with our demo truck so much that it seemed to not be loud at all. Then after about a 2 week break from it, it felt like it did when we first built it. however, I'm back to being the same way with it again so it is about time to rebuild the wall //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gifIt just confuses me... it seemed much louder the first day I got it. But you are correct. I could of very well just grown to it and not notice what it is anymore. I could probably tell a difference if any of my friends had systems... and 0 of them do =/