probably due to the dimensions of the cabin... hatchbacks give good response at a certain frequency, and an SUV might give better results at another frequency. Maybe what you heard was booming. My car is a minivan (Kia Carens) and when the subs hit, the driver hears the sub alright, but when i stick my head in the back...wow... my eyes are about to tear and the subs move excessively. Bass cancellation is massive...
I totaly agree that the trunk does make the difference. Also where and what the bass reflects off of makes a difference too. Of course glass is going to get a better bass rebound than sheet metal or carpet. Thats partly why hatchbacks hit harder in a wide range of boxes and subs.