Couple things;
1) only the fist number in the address is relevant.
2) Mach anomaly (may or may not still be with us in current versions) For me, Mach would not tolerate changing the address in the config unless I first zeroed the address, disabled the port and closed and restarted Mach. Upon restarting Mach, I could then enable the port, put in a new port address and Mach would use it. Note that this is just an observation and I do not know why it happens this way. I might speculate that this is because the port driver has a death grip on the port while running as a separate process outside Mach, but whatever the cause, I found you have to slap Mach in a face to get it to let go of the address it is clinging to before it will consider changing to a new port address.