Agreed, slice off a set amount of top and bottom scores for grading. That way a sustained set of scores will affect grading, not the odd one or two either way.
It's not like that score can't be used in the league, so it's recorded, and it would still be recorded in grading, as omitting it would mean the next highest or lowest score would be removed... but it won't affect the calculated grade unless a higher, lower or equal score is submitted.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep