XML for Extension Collection of Purchase Orgs on Materials Import

I am having a problem properly formatting some XML. We added an Extension Collection to the Material Master in Sourcing for holding a list of Purchase Org Objects. I have been trying to modify the standard XML PI uses when it receives a MAT_MAS IDoc. I have done many iterations of the XML. Some that succeed with Warnings and some that succeed, but don't add the Object to the Extension Collection. I have tried the following. How do I format the XML so I can add the Purchase Org Object to the Extension Collection?

Import Successful But empty row in Collection

<collections>

<WMT_PORGS>

<object classname="masterdata.POrg">

<fields>

<WMT_PORG>

<EXTERNAL_ID>CA01</EXTERNAL_ID>

<BUSINESS_SYSTEM>DR4CLNT420</BUSINESS_SYSTEM>

<DISPLAY_NAME>Purchasing Org CA</DISPLAY_NAME>

<DOCUMENT_DESCRIPTION>Purchasing Org CA</DOCUMENT_DESCRIPTION>

</WMT_PORG>

</fields>

</object>

</WMT_PORGS>

</collections>

Successful Import But empty row in Collection

<collections>

<WMT_PORGS>

<object classname="masterdata.POrg">

<EXTERNAL_ID>CA01</EXTERNAL_ID>

<BUSINESS_SYSTEM>DR4CLNT420</BUSINESS_SYSTEM>

<DISPLAY_NAME>Purchasing Org CA</DISPLAY_NAME>

<DOCUMENT_DESCRIPTION>Purchasing Org CA</DOCUMENT_DESCRIPTION>

</object>

</WMT_PORGS>

</collections>

Successful Import But empty row in Collection

<collections>

<WMT_PORGS>

<object>

<fields>

<WMT_PORG>

<object classname="masterdata.POrg">

<EXTERNAL_ID>CA01</EXTERNAL_ID>

<BUSINESS_SYSTEM>DR4CLNT420</BUSINESS_SYSTEM>

<DISPLAY_NAME>Purchasing Org CA</DISPLAY_NAME>

<DOCUMENT_DESCRIPTION>Purchasing Org CA</DOCUMENT_DESCRIPTION>

</object>

</WMT_PORG>

</fields>

</object>

</WMT_PORGS>

</collections>

Succeeded with Warnings But empty row in Collection

Succeeded with Warnings

..Record 1. Warning: ID: exception.common.importer.field.cannot_resolve_external_ref

..Record 1. Warning: Value for business system is missing. Enter a business system.

..Record 1. Warning: Referenced Master Data not found for field WMT_PORG : EXTERNAL_ID:CA01, LOGICAL_SYSTEM:null

<collections>

<WMT_PORGS>

<object classname="masterdata.POrg">

<fields>

<WMT_PORG>CA01</WMT_PORG>

</fields>

</object>

</WMT_PORGS>

</collections>

This is what I mean by "empty row in Collection"