I haven't gotten to play around with the idea that it's difficult to picture exactly what you want when transforming and actually get the results you want (unless your name is Grace) nearly as much as I've wanted to up to this point. Grace's mind is basically all set up and ready to go for precision dynamic morphing (which possibly includes certain additional talents as a side effect). Your average person, not so much.
Then again, Susan and Nanase are NOT average in a lot of ways that include the realm of smartness and the pants thereof. Might they have better luck?!?! <- (Get hyped)