Copy Pricing Cond. from PO to Billing Doc. in 3rd Party Sales

Question

Background
For Third Party Processing, the standard SAP "Document Flow" is:
Sales Order -> Purchase Order -> Invoice Receipt -> Billing Document
Question 1
We have this Third Party Model described above mplemented with my current customer.  Standard SAP Condition Type VPRS is in the SD Pricing Procedure and during Sales Order creation it is determined via Material Master.  However, after the Invoice Receipt is created against the PO, it appears that VPRS is redetermined in the Billing Document based off of the 'Cost' from a Condition Type in the PO. 
My question is as follows:  How does it 'know' to do this???  I do not see any code or calculation type in the Pricing Procedure that tells it to pull it from the condition type in the Purchase Order.  Where is this code - or - where is this functionality derived from in Pricing Configuration???
Question 2
This question is dependent on Question 1, but is it possible to pull other pricing values from the PO into a different Sales Order condition type(besides VPRS of course) using stricly Pricing Configuartion or do I have to code some sort of Calculation Type to do this? 
Thanks for any help here!
Mike

Answer 1

Hello Mike
Question 1:
It knows it from config as you rightly guessed. Let me quote from SAP help documentation:
Documentation for VPRS says "For a third-party business transaction, the costs are determined from the purchase order:"
If Customizing has been configured appropriately, the system determines the cost for third-party order processing from the value of the vendor invoice plus proportional statistic conditions (for example, cash discounts or statistical freight) from the purchase order in Materials Management.
The quantity indicator in the billing documentu2019s document flow then controls where the cost comes from. Activate indicator F in the Billing quantity field (billing quantity equals goods receipt quantity minus quantity already billed).
This is in copy control. VTFA - Item cat settings
Links:
http://help.sap.com/erp2005_ehp_04/helpdata/EN/d7/5cf0e89e5911d2959e00a0c9306794/frameset.htm
http://help.sap.com/erp2005_ehp_04/helpdata/EN/eb/85a078893811d2ac830000e8a5bd28/frameset.htm
Question 2:
I don't think it is  possible to pull other pricing values from the PO into a different Sales Order condition type using strictly Pricing Configuration. You will have to  code some sort of formula ( Alt. Cond. Base value/Alt. Condition Value)  to do this.
Hope this helps.