[Therion] Controlling map location on page

[Michael Perryman]

I'm just starting with Therion. I have the same problem as a user back 
in 2012:
     http://comments.gmane.org/gmane.comp.gis.therion/3066

When using "export map" my map is at the top right corner of the page, 
with much white space to left and bottom. I could not see a satisfactory 
resolution in the above thread, although I assume its possible (simple).

In the .th file I have defined:
  cs OSGB:SN
  fix 1.0 xxxx yyyy zzzz

and in a "layout definition" in the .th file I have tried some 
combinations along the lines of
cs OSGB:SN
origin xxxx yyyy zzzz metres (or grid-origin...)

but without any success in moving the map in the output pdf

Thanks for any pointers...