All great discussion.
Vortex Ring State requires you to be descending through your own downwash at very close to the vertical speed of the air being pumped out by the rotor. The downwash velocity from the rotor will depend on the power being developed at the time.
Classical requirement aside from the vertical speed is to be descending into that downwash - normally by descending straight down in a no wind situation, but also by being in a no wind situation by confusing groundspeed with airspeed (and actually being downwind and having zero airspeed, but some groundspeed).
Different aircraft will have different downwash velocities - light disk loading (i.e. large rotor diameter and light weight) will have a much lower downwash velocity than a small rotor diameter and high weight, and the low disk loading can actually get into trouble at a lower rate of descent than a high disk loading machine.
What is not common knowledge on the V-22 crash is that the rate of descent was extremely high- so high in fact that the lead aircraft, which did not get into vortex ring state, hit the ground so hard it was written off.
I've only ever been able to demonstrate VRS by doing with a tailwind, at altitude of course. Trying the same thing into wind from the same starting conditions results in something completely different and not VRS.