I am a crusty ole long line pilot here in Canada and have been looking straight down out of all kinds of different machines over the last 10,000 hrs or so.
Since production longlining is pretty much all I do in all kinds of terrain I am often dancing on the edge of conditions conducive to vortex ring or just simply mushing due to the aircraft simply not having enough power to do what I have asked of it.
To me the defintion of vortex ring is when I pull collective and my sink rate INCREASES. Doesn't matter much what my vertical speed is because its more about relative airflow. If I pull power and my ass gets LIGHTER in the seat its time for immediate corrective action. Some may call this "incipient vortex ring" vrs full blown VR. Labels dont seem to matter much when it happens at a few hundred feet.
If I pull power and my ass gets slightly heavier in the seat, but I am still decending faster or more than I want too, then to me that is settling with power. This could of course get ugly and turn into overpitching if you keep pulling collective. It could also turn into VR if your sink rate increases.
DMNH