I always find it very difficult to put a 300 into incipient vortex ring if flying into wind ( about 15 kts plus), unless you go backwards ( relative to the ground) as the wind has an equivlent of 15 kts fwd airspeed, helping to keep the disc into clean air thus no vortex ring or limited effect. Turn heli the other way and bring back to 15 kts airspeed ( downwind and relative to the ground) and the heli will easily get into vortex ring, as effectively you are in a hover and hence the disc will be in its own downwash as you descend.
Well thats my experience anyway