There seems to be a thing remaining from when the aluminium plates were merged. The signal input for aluminium plate is still for the unused aluminium plate when choosing what the belt should react to, so this setup doesn't shut it off when aluminium plates has reached 4k. (and is only one aluminium plate to choose from in the signal menu)
EDIT: I've done some more testing and found some other cases where the signals are wrong, look further down in comments.

