We have a problem with dots under 6% on our Flexo presses.
Anything lower than this just completely drops off...
so to cure that we set up a curve in photoshop to make any dots under 6% go up to that point.
I don't know if that helps or not.. but
here
http://www.box.net/shared/lnopp6vys6
Just load the preset in your
Layer>NewAdjLayer>Curves hit OK
then go to load preset and then use the file.
its the actual curve we use, it could give you an idea to make your own.
beauty of it is being able to adjust it w/o screwing up your image permanently.
sorry I'm not more precise..
maybe Vokaris could help you more.