I when it comes to the Tens, I am not sure at all about those details you ask. The electrical field across the neck meant that they didn't come up that far and for that I was so grateful.. it did give me some respite from having those awful migrations - but its something that needs to be be done almost constantly to stop them migrating that route... Geritol also believes that the high voltage he used killed some... but I have read in other places you would have to electricute yourself to kill the big critters.. so I'm not convinced that the TENS kills the big ones.
I know Geritol experimented with different positions and he understood the Science of it much better than me.