Hi David,
I checked the guide, it does not say that PI independent is possible with the RFX outside firewall scenario, the section is just a reference, where the PI independent documentation can be found. If you check note 1523906 which is about the bidder transfer in the RFX outside firewall scenario, you will find that PI is needed as well. Anyway it seems we might have a documentation error here, we will clarify this internally.
But your issue was not with the RFX response outside firewall, it was about ROS potential supplier transfer, and for ROS PI is mandatory. Otherwise no XML message will be generated from SRM to ROS once the transfer was done, and this will result in no emails sent out to the supplier with his logon data. Configuring PI is the only solution for your issue here.
regards
Zoltan