Currently, I can call SetIndexInParent to set the index of a hierarchy node in it's parent hierarchy, and I can call SetSortingValue to manuallly set a sorting value.

The problem I'm having is that after moving around child hierarchy nodes by setting their index in parent to + or - 1 the current index, the sorting values have become much smaller and my nodes aren't moving as expected (they can jump 2 places).
I'd rather not have to do a manual calculation repeating what's done in SetIndexInParent with the sorting values, I'd like to just call a method on the hierarchy node class to move the child up or down one in the parent's sorted list.