QTR-Quadtone RIP

I'm trying to create some curves for Epson Glossy and Semigloss for
my 1290s, but can't get rid of a vertical banding pattern which is 
showing up on the initial 100% Ink Pattern Page (in calibration
mode.) I've not seen this when printing to Matte paper, and have
tried numerous head alignment operations.  Also tried different 
settings in QTR; speed, resolution and dithers.

Anybody out there got any ideas or solutions?

I've searched this forum to no avail,

regards, Jamie Creed