What happens is that if you press R immediately after activating your Ult, outside of his range, Jhin will fire his first shot there. Meaning that he can fire his first shot behing him or basically everywhere. I am not sure if this happens on a normal or custom game, but it surely does on practice tool.
How to do it:
2)Go lvl 6 to unlock R
3)Press R to start your Ult and spam it out of the given range(Left,right,behind him) before Jhin takes his position.