There seems to be a lot of speculation in this thread by pilots that have never done any production long line work.
In my experience it is possible to enter "settling" with the three stated FAA parameters being met. Altitude and gross weight have had no effect in my experience. In fact most of my occurrences happened with an empty hook and I was trying to salvage a poor approach, a little fast, a little down wind and a little step. The termination has put skid marks in my shorts in a Lama, UH-1H, Jet Ranger, Hughes 500 and Allouette.
Nick refers to it as "over pitching" but I am unfamiliar with that term. I will tell you that the only solution is to increase airspeed with a quick cyclic move, usually to the 2 o'clock position for me. I am sure that to enter true, steady state Vortex Ring, Nick is correct. However when you are close to the ground with your line or the ship, just the beginnings are enough to ruin your day.
Go ask any old seismic pilot.