Correct me if I'm wrong. rport helps in the correction of bad headers caused by NAT, but freeswitch will still report the endpoint as UDP-NAT. If the end point itself is aware of NAT and does not send any headers containing RFC1918 addresses then freeswitch will report the endpoint as UDP.
And with some of our locations which are behind CGNAT even before the net reaches their modem, without rport turned on (yealink units) the phone can not even register to fusionpbx.