What you guys say the optimal depth is for developing quad power which would be useful for sprinters? Fraction above paaralel?(as in hip crease relative to top of knee joint).

Interested to hear your opinions...

I probably wouldn't do fronts at all. Sprinter stepups, bulgarian split squat jumps and weighted box jumps all seem like better choices to me.

As rilla says there are better choices for all out sprint performance, but if you're going to do fronts as an auxiliary exercise i'd b inclined to say full depth. You're going to recruit much more of the posterior chain and probably the quads to a greater degree also.

If you want to use Front Squats to help improve sprinting then maybe not worry so much about depth, but focus on doing them relatively light but as explosively as possible in the concentric phase... maybe into a little jump if it's comfortable or possible. Depth keep as normal which should be ATG.

Go Deeeep!

I don't think you're asking the right question to be honest. With fronts the limiting factor isn't the quads, so in a way you could argue that fronts isn't primarily a quad exercise. For maximal direct stimulation of the quad, you need to make it as easy on the core/supoorting muscles as possible. This means finding exercises where you position the weight comfortably and don't have to think about weight placement at all.
This means placing a lightish load on your shoulders where the bar can rest comfortably. Lightish weight means you'll be doing unilateral work. Compare fronts to fx splits - where do you fail when you fail? On splits, how many fails out of 100 is because you can't stay tight in your core? How many fails is pure quad failure?
On another note, aren't you by far one of the stronger sprinters? Shouldn't you be working more on explosive strength than absolute strength?