Three hooks?

That must be the obvious difference. I've only ever rigged with two.

The front hook is just there to tow the bait... in my experience, it rarely ever catches the fish. It's just basically there to hold the bait.

It's infinitely more likely that the second hook is the one that's gonna catch the fish. If tied short with the trailing hook placed within or alongside the bait (ahead of the tail), that hook is also gonna get taken deep when Mr Salmon tries to ingest your bait. That's where the standard mooching rig is going to incur the lion's share of mortal bleeders. Hanging the hook back well beyond the tail ensures the second hook is almost NEVER taken within the fish's mouth.

Going to a third "hangback" hook really isn't a hangback rigging at all.... it's just another hook added to an already lethal standard mooching rig.

Bottom line, the key to not mortally wounding fish when fishing ANY type of bait is to NOT bait the hook that is going to catch the fish.