I know you don't take "questionable" shots.
I do. Look bellow.
What about a shot that is just on the cusp of what your opinion of "questionable" is or perhaps maybe even bleeding into your "valid" range?
In that case, and not saying that I always follow what I am about to say, get a new plane and try again. You can pretty match tell if the guy is doing it on purpose after a few fights. In that case, stop fighting him or try to learn how to avoid that situation. It is good practice any way since that is what you will encounter in the MA.
For the most part when I do it, the other guy was either turning faster than I thought so when I started firing it was a 40 or 30 degree angle but by the time they exploded it was close to HO and they chose to remember that, I might have made a mistake and got trigger happy, believe it or not the bad guy did the same to me in fight prior to that, Lag ect.
The general rule is that they can do it to you but god forbid you fire at them while they are looking up at you
Some people think that if they can see you, you took a questionable shot.
My experience with dueling has been that everyone tries to pull as hard as they can to get into a HO situation in order to avoid getting shot so you get merge after merge in a HO situation hopping you avoid the collision until the rolling starts. Very easy to make a fight go long at that point since both guys are out of e and barely can keep their planes flying. Advantage in that situation comes in inches at a time.