TT - any scientific basis for the assumed difference in coefficient of friction between asphalt and grass? Any factor applied for the lentgh of the grass? Or the temperatures of the surfaces? Runways and roads seem to be designed to have a high coefficient of friction rather than a low one.
Whilst the proximity of the ground does affect the inflow angle I'm not sure that the friction (or lack of it) of the surface makes any difference to that.
I have heard many theories about how the type of surface affects the power required to hover but, other than recirculation, have never been able to measure any difference whatsoever and certainly none I would rely on in an emergency above and beyond that which the simple ground effect does bestow.
Nigel - as previously mentioned, operating in the HV curve and suffering an engine failure might not kill you but none of those events Sid has linked to have left the aircraft in any vague semblance of serviceability
Wonder if the insurers coughed up!