There are at least three possibilities:
a) You are bringing files into the RIP which have an amount of white at the top, and that area becomes part of the print job, which pushes the print objects farther into the page. This happens with PDF files most commonly.
b) There is a setting in the RIP (not sure which one you are running) which advances the media a distance before starting the print.
c) There is a setting in the printer itself (via the control panel) that is responsible for the advance. I don't know whether this model (310) has this option or not.