IDOC WPUBON problem

Hi, We are using WPUBON idoc type for Sales Inbound Posting. Previously we are not recieving the TAX and system was calculating  the tax maintained in sap. Now we need to add TAX on article level so we have populated segment E1WPB04 which is meant for Tax. But even though the TAX is coming with the Idoc properly system is considering  the default tax only