Balancing Diffs on a Cat SX

[Verde]

I have a Cat sx which I bought second hand, so I don't know the history etc. I decided recently to check the diff tightness and the front is a lot smoother that the rear. Firstly is that right as I don't really have a grasp of diff set ups?

Secondly I tried turning the allen screws in the dog bone cups with a view to balancing them up. However, doing it like this had no effect as any more slack on the rear and it just slips, and the front won't go any tighter. Am I doing it right?

Many thanks,
Jason.