Ah...didn't pick the Insteon thing! Thanks for that info.
Lockdown does have a few benefits (extra time) so in the meantime I've crafted set of aircon control page objects that more intuitively represent asian/australian aircon controllers...consolidated heat/cool set points, swing/sweep control de-humidfy & fan modes, plus constraining the temp ranges, I'm coopting several. of the available temp settings to achieve this so still in search of the missing indigo commands for this device!
This does mean the native indigo thermostat ui potentially generates confusing outcomes. I still think there's case for a plugin aircon controller that is modelled on the physical UI of a typical split-system aircon rather than whatever the standard Indigo device is derived from.