VPRS-based condition redetermined in return order (referencing billing doc)

Question

I have an issue with copy-control from invoice to return order.
I want the invoice pricing conditions to be copied unchanged to the return order.
This is similar to when creation the Sales order>Delivery>Billing Document.
I need to make a return order for the same amount as in the original sales order (naturally, we want to credit the same amount).
This works fine for all conditions, except for a VPRS-based condition, which is redetermined upon return order creation.
The VPRS-based condition should fetch the moving average price for the sales order only, not for the return order.
I have maintained copy control for billing document to sales order with pricing type 'G'
G: Copy pricing elements unchanged and redetermine taxes. The system
This works fine for Sales order --> Delivery --> Invoice, but not for Invoice --> Return order.
I would prefer not to use a formula, but I guess one alternative solution is to fetch the condition value from the original sales order if I cannot do this with customizing.
Let me know what you think about the forumla (VOFM) and if it is possible to achieve copy-control with unmodified condition values for the VPRS-condition.
Thanks!

Answer 1

Ok, thanks for your input!
I'm sharing my solution:
I implemented a new condition value formula for my pricing procedure:
VOFM>Formulas>Condition value
FORM FRM_KONDI_WERT_XXX.
  DATA: lv_kbetr TYPE kbetr,
        ls_vbfa  TYPE vbfa,
        lv_knumv TYPE knumv.
Get moving average price for return order from SO
The ZPRS pricing condition modifies price in return order
The value of ZPRS should be the same in return order and SO
  IF xkomv-kschl EQ 'ZPRS'.
Get sales order and position
    SELECT SINGLE vbelv posnv
      INTO corresponding fields of ls_vbfa
      FROM vbfa
      WHERE vbeln   EQ komp-vgbel  "invoice number
        AND posnn   EQ komp-vgpos  "invoice item
        AND vbtyp_n EQ 'M'         "invoice
        AND vbtyp_v EQ 'C'.        "order
    IF sy-subrc EQ 0.
Get sales order conditions key
      SELECT SINGLE knumv
        INTO lv_knumv
        FROM vbak
        WHERE vbeln EQ ls_vbfa-vbelv.
      IF sy-subrc EQ 0.
Get moving average price from sales order conditions
        SELECT SINGLE kbetr
          INTO lv_kbetr
          FROM konv
          WHERE knumv EQ lv_knumv
            AND kposn EQ ls_vbfa-posnv
            AND kschl EQ 'ZPRS'.
        IF sy-subrc EQ 0.
Recalculate condition values
          xkomv-kbetr = lv_kbetr.
          xkomv-kwert = ( lv_kbetr * komp-mgame / 1000 ).
          xkwert      = xkomv-kwert.
        ENDIF.
      ENDIF.
    ENDIF.
  ENDIF.
ENDFORM.