PurAmino + Alcohol Free Vanilla Extract (how much?)

We are currently adding PurAmino formula as a supplement to my wife’s dairy/soy-free breast milk to make 165mL bottles. We have no issues adding 20% PurAmino, but 25% was immediately rejected. I have heard that adding Vanilla Extract works well to mask the taste and smell of PurAmino. Has anyone worked out the science of how many drops of Vanilla helps? I guess we could be tasting it ourselves and go from there but any past experience shared would be immensely appreciated.