I suppose that depends on the claims you want to make. Let’s look at an example.
Suppose you have an in vitro experiment that shows active X at 2% gives some benefit. Well if you want to claim that benefit in your product you should use it at 2% in your formula. At least you could make an argument it really could deliver that benefit.
In truth, you should really test in vivo from your formula at the % actually used if you want to make the claim.
But if you word your claim in the right way, you can put a tiny fraction of the ingredient in the final formula and simply imply that it will deliver some claim.
But it would help if we had more information about the ingredient/benefit you are trying to deliver.