The location is poor because:
(1) The tweets are too far from the mids. There's no point source, and different frequencies which should reach your ears at the same time are not.
(2) The tweets are too close to your ears. You want the speakers in a car to be as far away from you as possible to help minimize the difference from your ears to the left and right speakers (equal distances are optimal).
(3) The tweets are behind you. As the common question goes "Do you turn your chair around when you go to a concert?" This makes for an extremely messed up front soundstage, especially with the mids mounted in front of you.
(4) I'm guessing that you're running your front and rear speakers in full-range in addition to the two pairs of tweets you've mounted up front and in back? You've got eight different speakers producing highs in your vehicle when only 2 are needed (maybe 4 if you've got whiney rear seat passengers, but I've never had complaints from back-seaters with just a pair up front). You've got highs bouncing every which way from every direction, not exactly idea for a good front soundstage and accurate sound.
You should try and come to one of the SVT Heart of Illinois car shows this summer and listen to Bob Johann's SVT and hear a phenomenal front soundstage. He's got 8" subs in the front doors and the mids/tweets mounted in custom kick panels. You could even listen to mine - you'd be surprised what kind of sound only 5 total drivers can produce (2 tweets, 2 mids, 1 sub).
