The reason people dont tend to use rear fill is because if you are trying to reproduce the recording as if it was performed the sounds should sound like its coming all from in front of you. Kinda like the recording was made in stereo so it should be reproduced in straight stereo. In such a small car, unless you just need it to be insainly loud then i would ditch the rear fill and spend the extra money as good as front speakers as you can get.