Little known fact-
The reason the low hover height on the HV curve is typically about 6-10' is that the FAA technique for testing the HV curve does not permit the collective to be lowered prior to it being raised.
So, when developing the low hover height point, you start increasing the height of the engine failure until you are at the point where following the engine failure you sit and wait while the aircraft falls, and then can only yank mightily on the lever to try to stop the rate of descent.
Obviously, those who are trained and prepared and proficient who hover at higher heights and know to lower the lever briskly first are doing something different than the published HV curve demonstrated.
This contributes to people treating the HV curve with less respect than it deserves.
And for Part 27 helicopters, the HV curve is not a limitation. Part 29, 10 passengers and more, it is a limitation unless you're using Category A procedures.