On the FortiGate firewall, address objects and virtual IPs (VIPs) can be set up with an interface. For address objects this has no technical relevance – the address objects simply only appear on policies if the appropriate interface is selected. But for virtual IPs, this setting has relevance on how connections are NATed. This can be problematic.
This is a small example on how to configure policy routes (also known as policy-based forwarding or policy-based routing) on a Fortinet firewall, which is really simple at all. Only one single configuration page and you’re done. ;)