mate if you're using a single hook rig, then i'd go through the upper lip for sure - jacks love to kill their prey head on. if you can though, also attach a stinger hook to the caudal region of the fish towards the tail. you can cover more ground then, as sometimes they'll go against their normal head first attack. try clipping part of the mullet's tail to give it an injured appearance and to control its swim path - i find some mullet are too hard to control and keep in the strike zone otherwise. let us know how you go mate.
cuzza