How can i keep planes in good SBDE numbers from the same air base?

I'm trying to keep some tac bombers and fighters in stacks of 5 to maximize state-based damage efficiency. They're in two stacks, 5 tac and 5 fighters each. I'll send one out to bomb a position, wait a bit, then send another stack out. Then I go afk. When I come back, they're in one massive group with terrible SBDE. Do I just have to put them at different air bases?