UNCTUOUS
A very well argued treatise on a little understood subject.
However you are incorrect in one area. Vortex Ring does occur in contra-rotating tandem helos. During a trial some five years ago by RWOETU(Rotary Wing Operational Evaluation and Training Unit) a pilot known to me experienced what was subsequently, positively confirmed as VR. It occurred during a very high (5000'+) hover. and was in all respects identical to a conventional Helo VR state. High ROD, Low IAS,Power applied. Since then the recommended recovery is as you stated, except that a bias towards the left side is helpful(clean, air to the advancing blades). I thought you might be interested.