Hi Brett,
The communication between RQM and RPT is via RPT Adapter by RQM which is owned by RPT team. An older documentation (  https://jazz.net/help-dev/clm/index.jsp?re=1&topic=/com.ibm.rational.test.qm.doc/topics/c_rpt_adapter.html&scope=null ) may help you with some clues about RPT. Pleas have a look.

Regarding additional information between RQM and its adapters, it can be passed between RQM and Adapters via following ways  -
  1. Execution Variables - If RQM Test Scripts wants to pass on some additional information regarding execution functional RPT scripts. See more about how it happens for Command Line Adapter (CLA) at here or at https://jazz.net/help-dev/clm/index.jsp?re=1&topic=/com.ibm.rational.test.qm.doc/topics/c_execvar_overview.html. Please note that this could be used mainly for information exchanges from RQM to RPT.
  2. Logs , Attachment files or links to Results - When the execution is completed, then logs, other form of files or reports links can be attached to the RQM Test results by the Functional script ( RPT in this case ). So RPT adapter can choose to upload the result back to RQM Test case result as attachment or link to results. See more about how this can be achieved for CLA at here. The would be applicable to RPT Adapter as well but for that you may have to connect to RPT adapter team.
  3. Custom Properties - You can use custom properties to populate information into the RQM execution results of your CLA tests. Weather RPT supports it or not for that you may have to connect with RPT adapter team. You can find more about Custom Properties in context of CLA at here.

In short, RPT adapter may make use of point 2 and point 3 to update the percentile information back to RQM execution result, however if it is available from RPT adapter or not that question is to be answered by RPT Adapter owners. If you need contact info on that, please let us know.

Thanks,
Abhishek