Where has the Use Outbound Address NAT Advanced Option Gone?

We're running SFOS 18.0.0 EAP1-Refresh1 and things seem to be going reasonably OK so far, until it came to setting up a new outbound MASQ on an alias IP.

Is it just me missing something or has the option which was previously available in Advanced > NAT & Routing for the Outbound Address on masquerades completely disappeared?

--Richard