Gordon, Whenever I use my "mover" I always try to drive it in reverse, ie. with the jockey wheel trailing. In softish going, if the j/w is leading, it tends to "dig-in" Also I find, as my mover is fitted in front of the axle, the rollers are below the centre of the wheel and are pulling the wheel upwards & tends to make firmer contact with the wheel when driving the van in reverse, the j/w just rides on the surface.
Just try pushing a wheel barrow over a soft surface, then try pulling it, then you will see what I mean.
Tankie