[Lmackattack]

Yes the trailers wheel base shrinks as the box goes up. The Idea is you back into your spot. Set the tractor brakes and then raise the box. As the box goes up it pulls the trailer axels close to the truck and the load starts to come out. Then you release the tractor brakes and when you lower the box it moves the tractor forward...kinda like an inch worm. It can help you get out of a soft spot where traction is limited. some people set the trailer and let it drag the truck back but I prefer walking the trailer out so the load spreads.

As long as you keep the truck and trailer straight when dumping you are fine. And actually you should never raise the box when the truck is not straight to the trailer. It's hard to see if it's leaning when you are on an angle?. Not to mention you should be backing in on a flat surface and pulling out in the same path.