Catfish Rig

I rig bluegills right behind the dorsal fin.  7/0 hooks.
 
What I've been told when I had a similar problem is that it's either small flats or channels playing with your bait.  Basically their mouths are too small to get the whole bait in it, the run, but you can't get a hook set alot of the time.
 
If it's a big cat, that fish has your bait in it's mouth almost instantly, set the hook hard, real hard, unless using circle hooks.

I like to hook my bait behind the dorsal on top.This way IMO the bait wants to try and swim away and looks livlier.I,ve messed around with stinger hook rigs a few times before.I ended up quitting after getting an increased amount of hangups.I agree thats it,s probaly smaller cats messing with your bait.I,d either keep it the way you have it and hope for a bigger fish or else size down your rig and find out what,s hitting on it.Are you sure theres bigger cats in the area your fishing?

I hook all live bait in the head.  Usually, because I have a habit of reeling baits in slowly.  If it is large enough, in one nostril and out the other.  Seems to keep them alive a lot longer.

I use chubs hooked in mouth. Sunfish or bluegills in back. Both on slip rig

Big egg sinker above a barrel swivel, big hook, big bait head hooked.