-geometry 1200x824
seems a bit big?
Ill have a play later.
EDIT:
Meh I got tied up. Perhaps tomorrow. nudge me! lest it again falls thru the cracks.
EDIT: that's the sizes of a DX - dpavlin - who wrote that script - has a DX IIRC.
Having a bit of a play now
Let's try... 600 x 800