For the ndgraphic, have an explicitly kwarg "graphic_kwargs" and store that. See how the graphic kwargs are handled for ndimage and positions. When the graphic gets re-created if the data is re-set, it uses the original kwargs.
In the add_nd_vectors helper method you can have size as a kwarg and put that in the dict along with any other graphic kwargs when you parse.

Sweet thanks, made the fixes to mirror what ndpositions does, lmkwyt