Mart,
Your analysis is correct, and is the bread and butter of NOTAR, but (you knew there is a but there!):
The airfoil only works when the downwash is on the tail cone. In as little as 6 knots of wind/aircraft speed, the wash moves considerably, and the airfoil on the cone is does not produce the anti-torque needed.
The first NOTAR actually lost yaw control in 6 knots rearward flight, so they invented the tip nozzle to fill in.
In the example we have worked, you must leave the tail rotor power where it is for some conditions that are in the hover. That is why NOTAR lifts about 2 passengers less than its tail rotor equipped clones.