If you fade 2 db to the right and 1 db to the rear it counters the imaging problem. distance between the listener and tweeters doesn't matter for imaging as long as levels are adjusted to match. Phasing issues arise when the distance between listener and speakers is different, which is why you want to try to keep your speakers about the same distance from you (not so much for imaging more for phasing), but I leave my oscilloscope in my sound studio, so I won't notice, besides there is a far greater phase shift between front and rear than there is left to right

if tweeters mounted on the pillars are angled correctly the sound stage should be about ear level. another fun fact about speakers mounted in the rear deck or on the dash board is that the treble out of such speakers is not designed to radiate directly, but to bounce off the glass.
I got rid of my kick panels for the same reasons you are getting rid of yours, that and I thought they sounded like crap, I had Sony 5.25" components in mine.