You also have consider the distance from the hitch to the trailer front axle and from the hitch to the tow vehicle rear axle will most likely be different. If you take 50 percent of the tongue weight off the vehicle rear axle, that 50 percent may be distributed differently to the remaining axles based the difference in length. Although you figure this out mathematically, it is easier to find closed weigh station where the scale is still operating and try different WDH hitch settings and their effects on your combination.