Fit problems printing clear film on HP Printer

hi folks,

we are having fit issues when printing on clear film material on our HP Designjet 5500ps.
i found a PDF manual online but didn't see anything about being able to adjust printing.
depending on the size of the print, it ranges from 1/32 to 1/8 under actual size.
clear film we are using is Graphix Clear HP.

anybody run into this? advice?

thanks in advance!
cesar