American Parkour

Ok, I've been practicing front flips in the only way I can at the moment: I jump onto the outer rail of my trampoline and flip onto the tramp. I can usually make it alright, but here's my question: Is learning to front flip off a rail harder than a larger flat surface, or are they the same? I'm wondering if I've skipped straight to a harder move, meaning I'm ready for a front flip on the ground or off a low object.