If those figures are correct, it may be a case of having 2 as a token measure so they can go to the ranges with them. There probably wasnt a lot of use for the in a home defence role unless the VDV started landing.
Home defence in our context was more about maintaining control of the population in crisis, and guarding establishments against sabotage. Ive read one of the reasons why John Nott was pushing for airmobile forces is that when the rest of BAOR collapsed, we might be able to bring something back to defend the country. Though im not sure an airmobile brigade would have gone very far.
the 81mm were meant for shooting illumination to spot looters
Im still trying to work out why they gave my father training on the 3.5 inch rocket launcher. Maybe they were frightened someone would hold up a bank.