Just to clarify a point. There is no requirement in a Part 27 helicopter to stay out of the HV curve. Part 29, 10 passengers or more, there is a limitation on it.
There is also no HV curve information for a descent situation - the HV curve is published for takeoff power at a heavy weight, high density altitude from the hover to the 'knee' of the curve.
So, there is no requirement to stay out of the avoid curve in a descent to landing. There is a requirement that the takeoff distance (measured and if published) as well as the recommended takeoff flight path stay clear of the HV, but nothing else.