Dubbing loop question

I've read the books and the online tutorials; but I'm having just s bit of
trouble with this dubbing loop thing. I'm hoping somebody's explanation can
shorten the learning curve a bit for me.

At a glance, this seems as though it should be a lot simpler than I'm
experiencing. I make the loop and open it with my fingers to insert the fur
dubbing. What I can't seem to manage is an even distribution of the
material nor keeping all of the material in place as I move down the loop.
Any tips?

Joe F.