If you want to know how well you're performing - check your league position in whatever league you're shooting (Winter League / GP Series ).
The grading system isn't a measure of performance, it's a prediction of performance for the next league. No mathematical formula can possibly get that prediction right all of the time because there are too many variables involved. It's an approximate estimate.
If you believe the prediction is wrong for you, the solution is to elect a higher grade. Anyone can shoot in AA grade if they wish, it just takes a quick email over to whoever is running the league you're shooting in.
If your scores in a league are much higher than anyone else's in your grade, there's a very good chance the initial prediction was wrong and it's down to your conscience to elect to shoot in a higher grade.
The systems falls down horribly when people talk about grades being earned and when shooters focus on a number which is meaningless. The maths isn't broken, the perception of what the number represents is broken.