My RB tuxie, Mortimer, aka Mr Fat Cat, used to get them right down the middle of his back. The only way I could deal with the clumps was to stay one step ahead of them. I just used a slicker brush down his back once a week or so, but if it did get to the clump stage, then I had to cut them out. Fortunately he tolerated me doing that without too many bloody bites. Wish I had that magic solution for you, but I don't.

I can see from your siggy pic that Crystal is quite the butterball!