@Kev Not sure if i am answering your question but the way i have it, i have a FW rule on WAN to allow traffic in on .65 IP and Port 7443
The rule is setup as source =any / Dest = single host and .65 IP. Dest Port =other 7443.
Under the StaticIP i have rule to allow all traffic
Source = StaticIP / Dest = any
I dont have any alias setup.
With the Configuration i have now, any pc connected to my Sophos UTM is now showing IP address of .65 on whoami vs before i got the standard DHCP IP address.
Hope that helps.