instead of blocks/amountOfValidBlocks
it should be
amountOfValidBlocks/blocks

my test case: I create a recipe of 1 wood + 1 dirt that yield stairs
according to this recipe
blocks = 2; amountOfValidBlocks = 1

with the original formula of blocks/amountOfValidBlocks the percentage will be 2
it supposed to be 0.5

True, good catch, fix merged