Consider this, if you haven't done it. You sit on the left side of the car. Your left speaker is something like 2' closer to you than the right speaker. Punch up into the empeg a left delay of approximately 50cm. Now put in a nice vocal CD and see if it doesn't give you a centered image.

In my experience with my old head deck, with a built in DSP, varying the image just "a little" left or right was very confusing. But when you really cranked on it, out of nowhere, there it was - the singer right in front of you.

I have a 3rd gen Eclipse, sonically not all that different from yours or any other small car really, and at about 41.some cm it's a dead on image right in front of me.