Each upgrade increases the hand size of stack inserters by 1.
This causes stack inserters to grab fewer items with the first several upgrades from this mod than without.
At stacking 2, belt stacking is 4 and the stack inserter grabs 16 items (4 stacks).
At stacking 3, belt stacking is 5 and the stack inserter says it will grab 17 items but it grabs 15 instead to be a multiple of the belt stack size.
I think the intended behavior is for the stack inserter to always grab 4 belt stacks.
