Non-Inventoried Item-where does the unit cost, vendor id come from?

Hello,

When using the "Purchase Orders Preview" window to create a PO from a SOP for a Non-Inventoried Item, where does the unit cost and vendor id come from?  

I thought it comes from the "item vendor master" table (iv00103)
But It appears like it comes from the detail line of the last saved PO generated for that non-inventoried item?
Can someone clarify for sure where it comes from?

We would like to specify the vendor id and cost for a non-inventoried item on the SOP document.
Is there a way to change this in setup somewhere? 

thanks,
Matt