In fact if you look at A and B class, there were actually more people that scored below their class cut off than actually scored within their class band. I would normally expect approx 70-80% of AA/A/B class shooters to shoot within their class band , 10-15% to shoot above it, and 10-15% below it. The scores need to fit in a bell curve. If the top scorer in each classification band is shooting within the band, then nobody will ever move up a classification, the only options are stay the same, or move down.
As a easy guide, look at the number of shooters that fall outside their class on the day. If there's more shooting below their classification cut off than above it then the shoot is set too hard, if there's more shooting above the cut off than below, then it's too easy.