Vertical descent above 300ft/mn down wind or low speed.... that's suffisant to gone VRS.
but not only...My first VRS was in approach with low speed and 150 ft/mn...But i was number 2 or 3 and 3 more chopper close behind me... The downwash of the other helicopters combined with my own put me in VRS
I was young pilot and have a old one Captain in the other seat : He push the stick in front and pitch down....I finish the approach number one