2 wheeled trailer - wheel position/weight distribution
Increasing the 'tongue' weight of the trailer (by moving the wheels to the rear, or only loading forward of the trailer wheels) does not increase the stability of the trailer or towing bike (or vehicle).  

Up to a point, it doesn't matter.  This is true for all trailers, bike or auto.

Trailers with extra tongue weight are more likely to cause the tire to 'wobble' on the rim about the contact patch.  The problem is especially bad in the case of an under inflated or flat tire.  (and if you ever have a flat while you are moving... you are riding a flat tire until you stop)

During braking operations, a properly designed trailer will push slightly down as it pushes forwards to increase the rear tire's down-force.  e.g. the hitch should allow for some small rotation in the Z axis and the hitch, ideally, should be slightly below the trailer's center of gravity (CG).  (think of it as pitching down as you stop)  Which is much better than trying to lift it off the ground, which would be the case with a negative tongue weight or hitch significantly above the trailer's CG.

If the trailer was designed for (or loaded for) a neutral or light tongue weight, it is safer.  If the trailer is heavy enough that it could skid the rear wheel during a turn, it should have a braking system or speed should be reduced.