FortiGate missing features

Hello I am currently deploying Fortiweb as REVERSE PROXY MODE behind a FortiGate. For this deployment, I need to create a virtual server on FortiGate. In addition, when creating the virtual server, I need to enable the "PRESERVE CLIENT IP" feature so that the port IP address of the FortiGate connected to the FortiWeb is not seen as the source IP address. However, I note that this feature is missing on my FortiGate. FortiGate 200E • Fw version : 6.0.5 FortiWeb 400D • Fw version : 6.03 So I want to know how I can deploy my FortiWeb without ever changing the firmware version of my FortiGate.