From inside the firewall all NiryoOne arms have unique IP address, but from outside the firewall only the host domain IP address is visible. A rule on the firewall translates outside traffic on port 9090 to one of the robot arms inside the firewall. Mapping port 9090 to all robots in the WiFi network would not work. All robots would receive the same instructions and would result in NiryoOne Studio getting return data from all of the arms.
This is why I mentioned creating additional ports (say in the range 41000-42000) firewall rules would map each port to a different robot on the WiFi. NiryoOne Studio would be able to connect to multiple robots from outside the firewall (was hoping to avoid creating the firewall rules).