Setting SenderID in TN_Parms for XML document types

Hi All,
I understand this is an old issue - discussed and solved by many. But after implementing what is suggested, it still does not work for me. I need to use webservice calling client to set the SenderID and create a processing rule based on that. Note that the SenderID is not in any of the XML tags that I can use XQL query. I understand I need to set the TN_Parms/SenderID as the external Id but when I supply an external Id ,say DUNS to the SenderID, bizDoc still reads ‘Unknown’ as the Sender.

What I am doing wrong?