I've had similar experiences with Strand hair and have tried a few things.  Increasing the number of strands per (unit) helps, though this will slow things down. 

You can also change the strand thickness, which may go some way to filling in those pesky gaps.  I'm not at my Poser PC at the moment, but I seem to remember you can change the base and tip width, if so then increasing the base width would be good :)

John

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