Funny I just went to asked the same question to this competition winning car audio store. The mgr. said that ideally you want the tweeter, at most, only six inches away from the mid, on the same plane ( common angle, flat area, etc.) and angled towards you. However, if you want more "hi"s then you can move the tweeter further up towards you. Most cars where you can hear the "hi"s this is the reason for that. Plus it also depends on how much extra stuff you want to do to your car (i.e. kickpanels, making a hole in your door, etc.) People place tweeters from kickpanels, to the doors, or next to the side views, and the pillars (towards the windsheild or away from it). He also mentioned placing them on your roof pointed down was a waste. One thing he did stress was dynomat in your doors that contain the speakers.