Same calculation, but you drop your advantage proportional to the distance from last frame. e.g., SFV, Guile s.mp is +4 on hit, 3 active frames. Last (3rd) frame is +6 on hit, 2nd frame is +5 on hit, and unsurprisingly, the first is +4.
Another way to think about it would be to take the base advantage, identify which frame you’re hitting with, add that frame number minus one to the base advantage.