Just speculation on my part and not really relevant if Adrian is right and it sounds as if he is but given the cost of gold toner nowadays it might pay you to use Fotomask on the non-print areas. It prevents toner penetrating the non-print area.

I have no idea how far Fotomask goes in terms of coverage v volume used. You'd need to check this out before being able to balance this cost against any saving on gold toner