Monitoring standby FortiGate

I currently have two FortiGate 60F devices running in an active-passive HA pair. I am monitoring the active device in N-Central via the management IP, but I am wondering what is the recommended method to monitor the standby unit as there is not a management IP of the standby device.

I was planning on monitoring fgHaSystemMode (OID: .1.3.6.1.4.1.12356.101.13.1.1) via SNMP and querying against the OID to ensure that the value of this 3 to match active-passive as I will know if the passive device is down if this value is either standalone or active-active.

Currently we are only monitoring the active device so we would not be aware if the secondary goes down