I'm going to just guess here. I think by placing it in front of the rear axle it devides some of the trailer weight over the front axle too? So, if you have a heavy weight trailer and move the hitch back behind the rear axle is it going to overload that rear axle? Will removing weight from the front axle affect handling/steering? I would guess the heavier the trailer the more likely it would be to cause problems for you. Adding the bike to the deck would probably counteract the weight shift from moving the hitch?
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio