From what you've said here, I still see no reason to think the supposed extra penetration effect isn't all in people's heads -- but I'm glad to hear you're researching it.
I think using other contact points than just the hands is a good idea, particularly for intestinal infestations, because electricity follows the path of least resistance. It's through induction and impedance that it is spread out to the rest of the body instead of just going straight through the chest. By using the feet or abdomen, you can make sure a current is going through the legs and lower body.
That said, the use of hand-held electrodes has been time-tested and apparently works very well. This morning I started coughing a little, so I got out my little $10 zapper with brass finger-rings attached to it's two alligator clips. I didn't time it, but the congestion disapeared within a few minutes, before I took them off.
I do not think big paddles or pipes are needed for the average person with a cough or cold, and I have never needed probiotics or had intestinal problems from my zapper. I speculate that the "near sterilization" Hulda mentions in her book is actually a flushing of the bowels, diarrhea triggered by the corpses from the initial die-off.