What about these two thoughts on power requirements in a downwind hover. As the tail wind acts on the horizontal stabilizer forcing the nose down, the cyclic has to be moved aft and therefore tilting the lift vector away from the vertical. Also the airflow from the tail rotor is blown toward the main rotor and effects the induced flow thru the rear of the disc. Both of these effects reduce the total rotor thrust and would require more applied power to maintain a hover height.
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