Muffin,
My answer would be that downwind a Robbie fuselage has barn door aerodynamics compared with into wind. Therefore you need a greater horizontal component of total rotor thrust to maintain position downwind than into wind. If you consider the still wind cyclic position as a datum, when hovering down wind, the cyclic would be further from the datum than when hovering into wind. In other words, the disc has to be tilted further towards the wind downwind to counter the greater drag on the airframe. Greater tilt means a decrease of the vertical component of rotor thrust that has to be countered with more collective.
I think that makes sense!