papersize settings for docbook formatting on dvi

[Felix von Delius]

Can someone give me a hint where to set different margin settings (i.e. a4) 
for formatting the FDP books to DVI/postscript? I couldn't figure out where 
to set the papersize and/or margins for docbook -> dvi formatting.  Even in 
the FDP primer I couldn't find a hint (maybe I will create a PR after 
figuring out where to set it).

Thanks for your help!

-Felix