honestly i haven't noticed a hitbox difference at all. either way thats the effectiveness of flick shots. you see where they are at, you flick and shoot and bang it hits. its almost instantaneous depending how quick you are at flick shotting.
also i have a very high sensitivity. its not great for normal weapons because when you need to move a tiny bit onto a tiny target obviously a higher sens is not ideal. but for scoping and flick shotting i find it very ideal.
either way it really doesn't matter what your sensitivity is, as long as you're used to it. i just don't have a lot of room to move my mouse, so a higher sens is necessary and i got used to it.
flick shotting is no joke, its no walk through the park, it takes a long time to get used to. you basically need to "feel" and know how hard to flick your mouse for each position you're in, and even the slight difference in distance changes that slightly etc. you really need a lot of practice to get great at it because there are so many variables.
so basically keep everything consistent (same mouse sens graphic settings same EVERYTHING) and practice. once you get used to it you'll notice it all come together.
scout is fun. i find it much much funner then regular weapons and when you're successful...oh man, just so super awesome.