resupply is actually one of the worst aspects of the game especially concerning strat targets. the players resupplying are almost never in contact with the enemy and contribute nothing to the fight beyond changing the mathematical dynamic and minimizing the effectiveness of attacking strategic targets often to the point that the bombers will not bother to hit said targets.
personally I think no strategic factory or instalation should be resuppliable. it adds nothing to the game and discourages bombers from bothering to hit strat targets. even the defenders are often to lazy to attack the bombers hitting strat targets and prefer to milk run strat with resupply after they leave.
resupply of bases is already so powerful to be on the point of game breaking but at least there is a remote chance of a c47 or m3 resupplying a base being shot at. but 75% of the time they are not even seen either.
resupplying factories, city and HQ should be removed.