Then you disincentivize attempts at stunting. Don't complain when your combats end up static with everyone lining up in a row and taking attack actions until the foes are dead.
It took me a long time to realize why combat in D&D devolves info "I move up, I attack, I hit, I do damage". That's why. If stunting for even simple benefits is hard to do, PC stop looking for things to stunt with. They don't climb the furniture, knock over objects, swing on objects or other cinematic flourishes. They opt for the safe and boring option, especially if their foes aren't making the same kind of blunders. It's taken a lot of retraining for myself and my players to look around the area they are fighting and use what's around them rather than slugging it out in a 5 ft square.
But if that's the kind of game you want, be my guest.