Science lady can pretty much adjust it anyway they want, so it's on them being dumb dumbs for not adjusting how to transform. Or Idk, maybe they are into that surprise factor lol.
But the main difference is that you also need to have an increased heart rate as well as as consuming female fluids. MC was being treated as a dog and MC was skittish so I guess he never really got his heart racing back then. He never really tried kissing Karen until the very end so there was no chance to transform.