Plug in truck bed or use plug in bumper for 5th wheel

My Ford has the optional "in bed" plug, and I use it all the time. On a prior trailer I had inadequate braking from the trailer, and in the process of checking things out, I found that the bed plug had about 1 volt less on the brake line (at full brake) than the bumper plug. The wiring harness went to the bumper first since that is standard, and then on to the bed. So, I assume that the longer wire and one more crimp connection increased the voltage drop.