Contract value is not getting update

Dear All,

   I'm adding sales item with reference of contract(value) through BAPI_SALESORDER_CHANGE, Item is adding in sales order,But item value is not getting realse from contract.Already sales order is created with reference of contract through create BAPI.

In BAPI Item structure im passing this parameter

           it_sales_items-ref_doc = contract no.
           it_sales_items-ref_doc_it = item no(contract)
           it_sales_items-ref_doc_ca = 'G'.

and 

           it_sales_itemsx-ref_doc = 'X'.
           it_sales_itemsx-ref_doc_it = 'X'.
           it_sales_itemsx-ref_doc_ca = 'X'.

Please suggest me if i need to pass more parameter?

if i create through standard screen contract value is getting update.