Ralph covers it pretty well here. Regardless of what interface you are trying to use, that interface you are accessing it by will need to allow the administrative access you are wanting. (https, ssh, telnet, ping, etc)
Chances are, unless you created a true OOBM network you will need to have the inside interface accessible.
Main issue as I discovered was that the Cluster Management Interface is in a sort of Null mode, not even root.
I reckon my diagram isn't clear, but in clear text from any hosts connected to any interfaces on a Firewall, there is no option you can reach the Firewall HA interface through the same Firewall.
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