IReport with Subreports and XML

I am using IReport 3.6.0. I have a main report and one subreport. The main report pulls the data from the XML file and displays it. The Subreport does this as well. Both reports use the same XML file with the XPath pointing to different places.
The subreports only purpose is to display comments (if any) under each of the listed fields generated in the main report.

The problem is that the main report never includes the data in the subreport.

the main report has the subreport with the expression
    $P{SUBREPORT_DIR} + "RelatedConceptSubReport.jasper"
and the datasource expression is
    $P{REPORT_CONNECTION}

the subreport jrxml file has the expression
    $P{SUBREPORT_DIR} + "RelatedConceptMaster.jasper"
and the same datasource expression.

I have created a parameter in each report with the same details
   COMMENTARY_NAME (with a value of) $F{commentaryName}

Do I need to do something else with the parameters that I have created?