QTR-Quadtone RIP

Hello,having a fair bit of sucess with an epson R800 & QTR.

However many prints have many small horizontal, almost tear like 
errors in the dither pattern, mainly in mid tones.

Have tried a number of settings, and settled on quality : best, 
dither : eventone.

The curve you use doesn't seem to affect the errors.

They are less prevalent in dense area, and non existent in the 
densest.

The one thing I haven't tried is the full range of dpi settings, any 
suggestions ?

I did however note the errors occur less often if you print an image 
at its native dpi setting without scaling in QTR.

The prints that are coming out of QTR are good though, just not 
competition level. And the tone control is excellent.

Any help much appreciated
cheers
Jonathan