Okay I think I have something I can live with now. Thanks BB and LMK (and anyone else who chimed in) for all the pointers.

It's not perfect, but as I said, I think that's down to the hair map, not the settings. (It wasn't intended to be used that way, but hey.... it saves me having a second M4 in the scene.)
Here is what I ended up with.
Will post the node settings in the next post.

Silke