When using multiple contacts for one customer, the wrong contact information is being defaulted into

When using multiple contacts for one customer, the wrong contact information is being defaulted into BI HDR when we create the invoices. For example; We setup Customer A with two contacts, one for email(direct invoicing) and one for print. In the billing plans we specify the correct contact using the bill to customer field but when we run the BI Intfc it uses whatever contact that's marked with the primary bill to default. So in the above example both invoices would email. How do we get the system to use the correct contact for billing?