"He who marches out of step hears another drum." ~ Ken Kesey
In the Illy gradient slider make sure your colors are at the extreme ends, and then slidethe middle adjuster towards the solid side. You can also use just one color and set the opacityof the opposite end to zero.That also looks like tones are being clipped maybe though, are you using a RIP at all?
Printing using Xante Screenwriter 5
Okay, that is real honest to goodness postscript for halftone manipulation strictly within Illy.