How to set up NAT for WAN ip address in case that ip address needs to be NATed to an LAN alias (LAN alias with real ip address)?

I have 2 aliases with real ip address on LAN zone, on WAN I have a private ip address 172.16.0.250 (gateway it's 172.16.0.253 on a cisco).
It seems that what I try doesn't work, on old UTM I have a simple NAT rule that is doing NAT from source 172.16.0.250 (WAN ip address) to 1.1.1.2 (where this 1.1.1.2 is the internet address behind cisco)
For the LAN access I have successfully created a firewall rule that does the NAT from 192.168.0.0/24 to 1.1.1.1 (where this 1.1.1.1 is the internet address behind cisco)

So the NAT for 1.1.1.1 works properly but the XG itself does't have internet access, if I try to connect on 1.1.1.2 from internet the connection works properly but if I initiate connections from XG it's not working at all
The only thing I came up was a simple iptables rule added on shell "iptables -t nat -I POSTROUTING -s 172.16.0.250 -j SNAT --to 1.1.1.2" and this works but I want to configure NAT from XG web not from linux shell :)

Did anyone had this issue or my configuration is something impossible to use on SFOS (please notice that on UTM9 my configuration it's working properly)

Thanks