I wouldn’t bother with 6x9 speakers in any car let alone an F/TF, they do nothing but screw the stereo imaging in the car, if rear speakers aren’t fitted to your car already I wouldn’t bother and spend the money on the front speakers.

 

The seperate tweeters mounted correctly up on the A pillar will be fine, what messes up the imaging and soundstage is having them in the middle of the mid bass unit down by your feet facing across the car.
There is no point putting them behind your head in the T bar though unless you just want volume and arent interested in the sound.
6x9 mids can sound pretty good if they are mounted correctly and in the right place, they have a decent cone area and can move some air.

 

I've already got 6x4" speakers in the rear. They aren't very good at all.

What are fount speakers? I only have front and rear ones. Is there somewhere else I can add another set of speakers then?

Andy - are you saying I'd be better off with a plain (integrated) rear 6x9" pair of speakers, rather than the separate tweeters, which could be reserved for the front pair of speakers, to improve the stereo-imaging?

 

I think he meant front
If you are interested in imaging, and soundstage etc the dont use rears at all, they pull the soundstage back and muddy the whole thing.
Fit lots of sound deadening to your doors and either fit those with the tweeters in the A pillars if possible, or at the very least into the top front of the door cards. You can fix them temporarily with blu tack and play with angling the tweets, a little difference in angle makes a big difference to the sound. If you havent bought them yet, go for normal circular comps, they are much easier to fit.
It still wont be great without going into time alignment and phasing etc, but it will make a difference.
If you want o get into the whole sound setup and get the best from your kit look around the TalkAudio site, but be warned, it can get expensive and takes time and effort
I spent 2 months sorting my crossover points and time alignment settings, then spend a lot of money on upgrading my kit to get the sound I wanted.

 

For inspiration looks at this install by Happychappy he completely did away with the rear speakers.

 

Inspiration?!

That's daunting!!!

I'll never be able to achieve that! I've got two left hands