I was playing with my trailer today believe it or not there was quite a difference on the ball weight form hitch on the ground to raised past horizontal.
So i got my 55kgs with the trailer horizontal (close to ball height) i done this by moving the boat back on the trailer to take weight off and of course forward to put weight on with it still on the scales. I moved mine back around 4" to take some off. (of course this method you have to be careful the boat is still supported correctly).
Hope this helps
neil