CUPS - margins on PDF in Ockular but none set in ppd file

Not sure if this is the best forum to ask, if not perhaps someone could suggest a better one?

I have an issue with CUPS printing. The .ppd file for the printer has the following entries for a 4x6" label (it’s a Zebra thermal label printer). The problem is that when I open a 4x6" label in PDF format in ocular, it always has 0.17" margins and prints incorrectly. The only workaround is to manually change the margins in Ockular (to zero) for every single label which is obviously a pain· Any ideas please?

*PageSize w288h432/4.00x6.00": "<</PageSize[288 432]/ImagingBBox null>>setpagedevice"
*PageRegion w288h432/4.00x6.00": "<</PageSize[288 432]/ImagingBBox null>>setpagedevice"
*ImageableArea w288h432/4.00x6.00": "0 0 288 432"
*PaperDimension w288h432/4.00x6.00": "288 432"