When sizing for HA, you must ensure that is sized identically. Mixing different VM sizes in an active-passive or active-active pair leads to unpredictable failover behavior and is not recommended.
If you'd like to narrow down your architecture, let me know: fortigate vm sizing azure
Azure imposes regional vCPU quotas on your subscription. If you plan to deploy multiple large FortiGate-VM instances, verify your quota before deployment. You can request increases from Microsoft if necessary. When sizing for HA, you must ensure that
: Deep packet inspection (DPI) and SSL/TLS inspection significantly increase CPU load. For example, one user's browsing and file downloading can consume up to 12% of a single CPU core when deep inspection is active. When sizing for HA