As of now, it is pointless to attack a HQ because before you even leave the sector, supplies are already being dropped.
Either:
1. Make it un-resuppliable
2. Increase the amount of supplies needed, like A LOT.
3. Place a "Resupplying Factory" at the strats or next to it. If you take that down, all resupplies are disabled. (Or supplies, both GV and field, will only be available by C47.