Territory Management, Assign Territories, "Mailing country" not available to create rule?

Territory Management, Assign Territories, "Mailing country" not available to create rule?

Hi,

I am trying to get territories (based on countries) to be set automatically when I convert my leads to contacts.  In the lead and contact I have the field "Mailing country" but to create rules I only have "Billing Country" and "Shipping Country" avaliable which is probably why my assignment doesn't work. How come I can't set territory based on "Mailing country" ?, Any workarounds