With the CG too far forward some planes refuse to snap, and usually if they do it's more of a wallow than a true snap. I have a nose heavy RC Nobler that will not snap, but some of that could be due to the ukie type coupled flaps... that is the flaps go down with up elevator and vice versa. There may be designs that will snap better (or worse, depending on your point of view) nose heavy, but I've not encountered any.