So, I seem to have solved this for the the A320neo and A321neo default aircraft, and the Fenix 319/20/21 by changing the throttle axis assignment from Throttle Axis 1 (0 to 100%) to Throttle Axis 1.
Suddenly the calibration works exactly as expected for all of these aircraft.
I’m not sure why it had defaulted to the 0 to 100% axis (I seem to remember this was needed in 2020, at least for the Fenix?), but it seems that Just Throttle 1 and Throttle 2 are the correct bindings.
Hope this helps others?