Hi Amelia,
I have the canon xh-a1 and several accessories attached to it. When I first tried balancing it I noticed putting the camera's center of gravity right over the post seemed to work better. When I tried it with it 3/4 " behind the post I never was able to achieve dynamic balance. I think the 3/4" rule is just a starting point.
I would try getting it with the camera mounted at different positions, just make sure that you have the camera's fore, aft, left and right CG located fairly well.
It may take some patience. However I have also learned that going crazy with dynamic balance is not necessary. As long as the camera is fairly stable when you spin it you should be good to go.