The current isn't passed down the line. It radiates that far and further in water, depending on the mineral content (conductivity) of the water. My original testing was done with a 30 ft test trough. I was measuring how far away I could detect the voltage. In salt water, the voltage only dropped by a couple of percent at 30 ft. In fresh water (Comox Lake tap water), the voltage dropped 30% for every 10 ft of separation. Later on, we had a boil advisory, so I took my equipment to Comox Lake marina. I took measurements out to 140 ft, which was the length of the dock. I could still read the lure voltage at about 3/4 of the original value. If I can read it, so can the fish. That indicates the range of conductivity that can be experienced in fresh water.
I continue to say to anglers that, if you know someone who has a non-fishy boat, they can't catch fish even past 200 ft depth. So, if the negative, repelling sensation can be felt by fish at those depths, they can also sense the attracting, positive voltage field coming from a properly tuned boat.
My 3 trollers all had black boxes, and I can say with confidence that, as long as the boat was properly bonded and zinced, my black boxes had little effect on my catch rates. I commonly fished 40 fathoms of wire, and down as much as 70 fathoms. The boats that had lesser hull signature values saw more success by using black boxes to send voltage down the wires.
Stick with the braid, simply for less blowback. I will be doing an article fir tha Island Fishing Magazine for the March issue. I will post a link to the online version, once it is published.