I don't know how I can help, but I usually figure out how fast or slow I should press JF 4AAAAA. The only reason why I tend to get it most times, is because I had to go by a rhythm. I press the A with the palm of my thumb at a not so fast yet not so slow pace.
I found my rythnm by setting the computer on all block. I kept doing 4AAAAA by listening to the guard hits and inputing it at the right time. I don't know but it worked for me.