NAT Manager

I don't understand what the NAT manager is asking me for.
 
I have some servers, let's take the Linux box as an example. It is on a
private network at 172.17.2.31. There is a hardware firewall between it
and the internet (a Juniper Netscreen SSG-520, if that matters). This
firewall is configured to map the IP address 1.2.3.4 back to the
Linux box. (The firewall also has rules permitting/restricting the
various services from various places.)
 
I have entered the NAT manager and entered the External IP address as
1.2.3.4 to 4, and the Internal IP Mask as 172.17.2.31. However
the Hosting Controller system still wants to refer to the system by its
internal IP address, not as the IP address that the system acts as on
the Internet. This will confuse customers, I think.
 
Further confusing the issue is the documentation, which appears to show
a private 192.168 address as the External IP, and 255.255.255.255. as the
Internal IP Mask.
 
How do I configure the NAT manager to present Internet IPs to customers?

OK, partial answer.

If you set up the NAT as I have done in the example, the external address is the one used in the DNS zones generated by HC.  This proves that the NAT manager understands the link between the internal and external addresses.

The example in the documentation is rubbish.

However, HC still presents internal IP addresses to the customer, which I think will be very confusing.