Additionally the blades of the Fenestron have a rather large camber also improving behaviour at high AoA. Therefore I tend to believe that it will create meaningful yaw/torque probably down to quite low RPM's.
I don't believe this to be correct.
So how would you explain that in the event of a tail rotor
control failure, where the tail rotor blades are stuck at fixed pitch, resulting in the aircraft yawing off heading on the ground during a running landing, bleeding off main rotor rpm has been shown to reduce tail rotor effectiveness and bring the aircraft back on heading? Unless there is a tail rotor control failure, the pilot can still "fly" the tail rotor with his yaw pedals.
Also, a known result of reducing rotor rpm too far in "normal flight" is loss of tail rotor effectiveness.