To publish the WebAdmin portal via the WAF you need to add a virtual host for NAT.
Traffic from: your Firewall
Service: the port from you WebAdmin portal (4444)
Going to: the virtual host (add a host and choose a available internal IP address)
Destination: your Firewall
Service: the port from you WebAdmin portal (4444)
Add a new real Webserver at the Webserver Protection section
Host: the virtual host from before
Type: HTTPS
Port: the port from you WebAdmin portal (4444)
Add a new Virtual Webserver at the Webserver Protection section
Interface: your WAN interface
Domains: choose the certificate for your Domain
Real Webserver: choose the Webserver from before
Don´t forget to enable every created item!