I have a 3220.
It looks like you cannot force HA1 onto the dataplane interfaces (you can for HA2) on the larger firewalls.
I tried making eth1/18 (fiber) an HA interface, but it would not let me select the interface in the HA1 config (it was an option for HA2). Same behavior on a 5200 series.
I know there are sometimes behind the curtains things that can be done, but wanted to check here to see if I was SOL or if there is something I am missing.