That kind of shot comes down to tracking the bogie in a side or up view, while guiding your nose so it will be pointing at their future flight path. It is 80% a blind shot (ie. not viewing through the gunsight). Either you guessed right and they are going to cross through your guns or not. A snapshot by definition is just a very brief opportunity to throw some lead in their crossing flight path.
As far as the reversal/barrel roll defense/(converting a flight path overshoot into a 3-9 line overshoot)...Unless the attacker goes for the shot on you hook line and sinker, it is unlikely you will have much of a shot opportunity on them when you exit. My point being, you can do everything perfect, and not have a short range shot because the bogie didn't cooperate. If you are consistantly denying them a shot, and are in a tail chase a few seconds later, it's a good start. From there it comes down to fine tuning the angles (on the fly), and narrowing the margin that their shot misses you by (drawing them in very close). This comes with time.
