Need help getting my hip powered "jab" right

[OMGWTF]

Put an X on your heavy bag. The jab hits the X on an upward trajectory, the right on a downward path. Same spot though. If the second straight punch is down, the next is up. But to the same target.

Thanks grey i still dont understand, lets say the right cross hits the bag at a spot we will label and mark X, then when we come back with a hip powered left jab how many fists distance to the right will the left hit, will it be 0 as in the same exact spot or 1,2,3,4 fists distance over

Also why would the cross come down and the jab up is it cause u slip with the cross