Prouty, R., Helicopter Performance Stability, and Control, 1986.
On page 306, Prouty estimates the total equivalent flat plate area of an example UH-60 sized rotorcraft to be 19.3 ft-sq (zero angle of attack). The contribution of the horizontal stabilator to the total drag is estimated to be 0.2 ft-sq. or roughly 1% of the total area at 115 kts. So the contribution of the horizontal stabilizer is really insignificant.
I thought page 296 might be of interest:
