I can easily add my 200 lbs. of my PUP tongue weight to my F-150 without a noticeable change to the rear, I suppose if I use a laser level I might see a 1/2 or maybe even a 1 inch of drop.
My point is, there is nothing mystical about a WD hitch, you do what the hitch maker says to do. I my case I add the 750 lbs. of TT's tongue weight to my F-150 and it sags like a wet noodle; I adjust the WD hitch to 8 or 9 links depending on how heavy the TT is loaded and my rig is level.
Exactly how level? Exactly how many lbs. of tongue weight remain? Well according to the CAT scales there is about as much as 500 lbs. difference in the TT rear axel weight with the TT loaded for the road.
Early on I played with the number of links and how it was riding but it was more tail chasing than it was worth. 30,00 miles later I was back to what the technician that set up the TT hitch recommended, "Adjust it so it look level and you are good to go."
There is no particular hitch ball height, in my hitch installation the ball was located about an inch above the level TT's ball socket.