Security Rating - Interface Classification - SSL-VPN tunnel interface (ssl.root)

I'm working on a 60E FortiGate firewall that was recently upgraded to 6.0.2. When I run the Security Rating it says that all interfaces should be classified as LAN, WAN, or DMZ. We have an interface SSL-VPN tunnel interface (ssl.root) that is not classified. What classification should this interface have, LAN, WAN, or DMZ? How is this classification set?