I've got the same problem. I only starting to do some taps, trying to be more aggressive with my bike. Cannot do vertical hooks too, yesterday me and friends were practicing it on a massive bin with two pallets high run up. I slamed into into it so fast...heh. And finaly done it! But there was a pallet on the side to it though, about 70-80 degre angle, so it was a bit easier that vertical wall. Just need practice more...