Longer Fletching will have very little effect of the arrows FOC% unless you are too light up front to begin with.

you want enough fletch to keep your arrow stable in flight but not so mutch that it will cause so mutch drag that it slows down the arrow.

If you are using field points or mechanical heads you can get away with using short fletch arrows.

But with broadheads you basically have the same thing on the front as on the back of the arrow the problem with being up front is that the Broadhead will steer the arrow instead of creating drag. this is where a 4" to 5" fletch works better than short fletch.