The postscript file generated from troff output by aux/tr2post doesn't
dictate the paper size. The postscript prologue (copied from
/sys/lib/postscript/prologues/dpost.ps) includes a routine
/pagedimensions which finds the actual page boundaries (clippath) from
the runtime environment (ie the postscript interpreter), and tries to
centre the printed material on the page. The paper size is selected
when you display or print the postscript file, for example using the
'-sPAPERSIZE=' command option for ghostscript or sending the file to a
real A0 postscript printer [must be a big beast].
In the case of page(1) with the '-b' option, and possibly other
postscript display programs, the size of the "paper" can be set by
including a BoundingBox definition at the beginning of your postscript
file as described in the 9fans item you referred to. For A0, this
would be
%%BoundingBox: 0 0 2384 3370
In your simple example of raw troff using '.ps 144', you should also
set '.vs 144' so the text won't be cut off at the top.
