But FP, as you reduce the downwash on the tail boom, you also reduce the downwash on the fuselage that is forward of the rotormast and on many aircraft that is of a bigger area than the tail boom.
Nick, I am sure what you say is right, but only once the RoD is established - the nose down pitch when lowering the lever is instantaneous - the effect of the tail stabiliser surely is most apparent after the nose has dropped, the speed has increased and then the change in AoA on the stabiliser acts to bring the nose back up, giving speed stability.
Especially since most horizontal stabilisers are upside down wings and an increase in AoA will give a pitch nose up.