Dont put them on the B-pillars. That'll result in your mid's and your tweeters being over 1m apart from one another, when you want them as close together as possible.
The optimum location is down in the corner of your footwells, facing upwards which then creates a nice 'rainbow' of sound imaging. However, otherwise either mould them into the A-pillars, or put them in the corners of the dash, firing diagonally accross the car. Tweeters where the mirror plastic is can also work well.
Basically, put some bluetac on the tweeter, and keep trying positions until you find one that you like.