Well, I finally got Auto Hover to work ...
DCS Stable version 2.8.7.42718, Microsoft Force Feedback2
Fuel Flow not mapped. Pitch and Roll axes linear with deadband 5 (I think this is critical for me, I'll investigate reducing the deadbands)
Hot start on ground. Set NADIR mode to Terre and NADIR parameter to VS. Lift off to approx 3m (10ft). Achieve stable hover (with slight movement).
No trim adjustment and setting.
Engage Auto Hover (key bind 'Q'). CVS indicator illuminates (below Fuel Flow switch 'POMPE')
Hands off joystick. Helicopter achieves wobbly, yawing hover. Adjust Yaw (using Z and X keys). Helicopter settles into the sliding hover within the box.
Phew!
Joystick still functions for gentle inputs, helicopter returns to position when released.