The Ford factory install is higher on the fender, but it has a big surround plastic box that extends the depth (at least on the super duty).
I ended up going high, right next to the tailgate above the taillight. Plenty of depth on the super duty anyway, and it was a snap to remove the taillight to route the wiring down to bumper. I bought the type that is prewired with a T-tap that intercepts the bumper plug in the back so both work.
I had to go where I am because I have the factory bed extender racks that fold up in the space behind the fender well. The spot actually turned out to be ideal to reach when hooking up.