10 to 15% is good for loads under 8,000, but you do have to take account of the vehicles load capacity as well as the hitch capacity, too. Many vehicles can pull a great deal more than they can carry. A 1 ton dually still has limits, as do receiver hitches, and thats in a "perfect" world. If Goobers son Harold installed it on the truck, all bets are off. Check the attachment. Once you have a half ton on the ball, you can start moving the CG aft so tongue weight doesn't continue to climb. You certainly dont need 15% of 20K tongue weight on a receiver hitch ball.