I think thats it. The placement of the speakers in the car greatly affect what you hear and how you hear it. Just mess with the fader on the deck or amp to get more sound coming from the fronts. Thats what I did on my Civic and now I get almost equal sound distribution, I hear my fronts a little more though, but I would rather hear the fronts more than the rears.

The placement thing is probably it because I also had this same issue with the home audio system. It was a pain in the @$$ to fix.