Think of them more as a distributed hub/switch.
the 'switch' has only one ID.... with many ports internally connected
Yours are connected by mains wiring.
Although you can talk to the one unit you are connected to (or sometimes a master unit), you don't talk to the others directly - they use their own inter-unit protocol for that.
often their is a config S/w specially to allow it (over and above the internal menu) - useful for adding more units to the collective identity.