My manual hitch maker says this.
WARNING !!!
"Never tow trailers in highway or high speed conditions with KWIK-SLIDE in the Maneuvering Position (rearward of the rear axle)! Towing with the trailer king pin rearward of rear truck axle can affect weight distribution and may interfere with the towing vehicle’s handling and response characteristics. Poor handling and response characteristics could result in death or serious injury."
I looked at several manual hitch makers website and they all said this or similar wording.