Whoa... I'm just a simple engineer, not a trailer designer. But even with my total lack of experience on the subject, I can easily see that deck pivot and axle location (i.e. tongue weight) need not have anything to do with one another. You can place the axles aft of the deck pivot, to maintain target tongue weight, even if the pivot is at 50% of bed/deck length. There is the issue of hitting the rear axle at maximum pivot angle, if pivot height/angle don't allow for it, but that problem is solvable, or a compromise can be found somewhere between ideal and the extreme of placing the axles at 50% bed length.