I think I'd want to get the exact measurement if you can as this is a somewhat critical part of getting your WD hitch to perform properly. Perhaps someone with that exact model can help you. Or your dealer? Generally, the top of the ball should be about 1" higher than the inside/top of your coupler measured when the trailer is level and on a level surface.
2012 F150 FX4 Ecoboost, 2016 Surveyor 274BHS
2003 Yamaha FJR1300, Demco Premiere Slider
1969 John Deere 1020, 1940 Ford 9N, 1948 Ford 8N
Jonsered 535, Can of WD-40, Duct Tape
Red Green coffee mugs