V X;
From many a manual; You need 300-1500(transport says 500-1500, military says 300 1500 and believe that number is more accurate) fpm rate of descent, low airspeed <20, and POWER applied, have been in vortex ring many a time with no sling load and little power, is all a ratio to how high the rate of descent is. In fact have had arguments with pilots who believe that it is easier to encounter VR state with unloaded aircraft, my suggestion to them is to watch the vsi sometime while on final with an empty line, not abnormal to sell 700-1000 fpm rate of desc, add a little power and yippie.
So to exit the situation one must break the 3 sided chain by either reducing the power to auto(doubtful but can be done if room permits), getting airspeed(usually the best method-cyclic in direction of descent) or by getting rid of rate of descent(usually impossible unless you have room). Lot of seismic drivers over the prairies will just hold power and wait, she stops in about a 10 foot hover, I don't have the balls to try am sorry.
Dammy:
Biggest catcher of pilots is working the upflow side of hill, where there is an equivalent rate of descent in a hover. 5 mph of wind vertical up mountain is the same as 440 fpm rate of descent, all it takes is to pull into hover with slight descent and no forward airspeed and bingo, good thing is that you are able to get out of VR more easily in uplow so can regroup and try again. Many days I have rather worked the downflow side of hill due to this.
My 4 cents
sc