> I expected to see equal amounts of vertical space above > and below.
Indeed, that would be more aesthetic. I have no experience with mom at all, so you'd best wait to hear from Peter or one of the other gurus. I can only offer a quick hack, but not really informed advice: If you set .nr #START 0 after .START, it fixes your particular problem here (see definition of DO_QUOTE in om.tmac). Whatever collateral damage this creates I don't know.
