Konica Minolta 1350w PagePro and printing non-letter size media

[tj]

I am confused about how to get inkscape, xdf, etc to print correctly on anything other than letter (8.5x11 inch) paper.
In inkscape I ste my page size to be 5.5"wx3.5"h, postcard, and do my work. However, when I try to print it prints on where would be the upper left hand corner of a letter page. And, since the 1350w feeds paper relative to the center, it would miss the card size stock completely.
I export it as a .pdf doc, open it in xpdf to print selecting the Minolta ppd supplied QSL, 3.5x5.5, media. It now prints in the center, but it is centered on both vertical and horizontal, i.e. dead center, on a letter size media. Once again missing the card stock.

so, hoe on a Konica Minolta 1350w PagePro do I get it print correctly o n anything other than letter.

tj