The first overboots we worked with the soles and heel were moulded flat and the bonder that joined upper to sole did not touch the heel part, the lacing was intended to pull it into shape around the heel of the boot. It was discovered, when squaddies tested them, that the overboot gradually moved out of position.
The next design still had the flat molded sole but the bonder had to position and seal all around the heel flap. As long as the operator placed the uncured butyl joining tape correctly the seal was good but the join needed to be trimmed.
The MOD then asked if the heel could be molded upright, this was done successfully by a company, who's name escapes me, in Birmingham and they got the contract. The bonding machine in the picture I posted was the first prototype of the machines we supplied to enable them to fulfill the contract.