Freight terms not editable in receipt header. (ERS/SBI using shipping date as invoice date)

Hello,

I would like to start using self billing invoices (SBI) for a particular vendor. I want to use the shipping date (as opposed to the receipt date) as the invoice date. I have set the SBI options to use the freight terms to determing the invoice date (for both the business unit and for the vendor location). I have defined a specific freight term code in the vendor settings. When I create a requisition (based on an item) through eProcurement and source it to a purchase order, the purchase order has the correct freight terms code in the schedule line.