in the moon event we only had one item to grind for, but since there are multiple items they have different drops rates across each battle

if you're trying to get pumpkins to drop, you can only get them from the 40ap
bats are more frequent in the 30ap
candles are good in the 20ap since you don't have to worry about them competing for bats and pumpkins
and if all you want is cupcakes you could theoretically grind the 10ap