Dont make it complicated.....keep the CPSA Classes ie AAA, AA, A, B etc
If AAA is 87% + then anyone who shoots 87% of the course score (Course par) call it what you want then thats how there classified wether they break 50 clays or 90 it doesnt matter, likewise for all the other classes.
Then you get a true reflection of each and everyones ability wether they shoot easy or hard courses.
Update it everytime they shoot and you will then get a proper classification system...how you choose to reward the classes is up to you..but it will certainly stop any score manipulation etc. Like Mr P said you can have a purple day reap the benifits but at least this way you wont not be penalised for the next 5 years because of it as it the next shoot youre back down where you should be.