When it comes to a confidence break down in changed situations I belive changing your aiming method is not the cure,because the aiming method is not the real issue.
The real issue is the change in confidence due to unfamiliar pressures.
If a person has an aiming system that works for them in everyday situations but not during unfamiliar situations,then the answer is to address the situation,not the aiming system.
Those guys that are doing well in competition aren't doing so just because of their aiming methods,their doing it because they have confidence in what their doing.
You can learn a new aiming method,,,but the confidence thing is still going to be there.
Maybe stick to what you know for aiming,but work on becoming more relaxed and confident in unfamiliar situations.
I won't bother going into my own breathing tech' because most trad shooters treat it like some kind of evil black magic or a joke,but if you do a bit of research on target archery breathing methods you'll find most of it is about lowering your heart rate,becoming calm,relaxed,confident, and shooting better because of it.
Good luck.