Strat targets should not be able to be supplied by forward bases.
Cities and factories build forward based (e.g. airfields, vehicle fields and ports), not the other way around. The fact that this increadibly gamey feature remains goes a long, long ways towards making level bombers useless.
You didn't see London being supplied from Biggin Hill or Sweinfurt from a local airfield. It makes no sense. The sheer ammount of supplies needed to rebuild a city or factory precludes the ability to resupply them with halftracks and C-47s.
Resupplyable airfields, vehicle bases and ports are a great gameplay addition. Resupplyable strategic assets are a terrible gameplay addition.