Oh that one is an side scroller. My method only works with a top down shooter since it calculates the straigth line and not a curve.
The easiest way is to use the gravity parameter from the bullet behavior, but that does not give you much creative freedom.
Nevertheless, you should take a look at it:
c3p file: 1drv.ms/u/s!Ap_-qxoGKbDccDi07YUVviB2-1k
Edit: I forgot that you want to aim at an object and the arrow should fly different distances. maybe you can use the tip anyway. You should stick to the tutorial you posted.