In response to the 300 fpm descent for VRS, I find that generally speaking you need a lot more then that.....however,I am a guy that has experienced I-VRS several times with the rate of descent at Zero, I know a few others that have had the same experience......The conditions condusive to this situation are rare, but some in the industry will come across it from time to time....Hovering at the top of a cliff face, with a line on, air coming up at you from below, low power, tail is twitching around, pull up just a smidge on the pole and the bottom drops out. Gets the heart pumping when your that close to the ground.......