With Akali I honestly throw my shit in the wrong direction a couple times a day because I can't tap to cast in direction of movement.
For some reason it seems like my kunai launch off into nowhere all the time now and I don't remember it being that way before.
But also, I've been playing with Diamond and Master players and the window to do stuff is way smaller.
This sounds like your button deadzone is too low, so when you are trying to tap cast your minor finger movement is interpreted as aiming. I'd suggest tinkering with that a bit and see how it feels.