3top,
Nick did fly the S-69. He may be tied up (kinky
), so here are some answers to your questions. Nick may wish to elaborate or correct them, later.
- The angle of attack on the retreating bladeis reduced, just as you suggest. But, unlike the CarterCopter, the additional load is taken by the advancing blades, not by a pair of wings. The two rotors are counter-rotating and their hubs and blades are very stiff. This allows the advancing blades, on both sides of the craft, to accept the load with minimal flapping.
- The act of loading the advancing blades more than the retreating blades takes place at all forward speeds. This is the reason it is called the Advancing Blade Concept.
- The craft had two methods of adjusting the advancing/retreating loading ratio. One was opposed lateral cyclic and the other was in-flight changing of the phase angle [Gamma]. I think that Gamma was the only one that they used. At the initiation of forward flight, Gamma would have a very low value. As the speed increased, the phase angle was increased to assure that the blade tips of the two rotors did not get too close to each other.
The rotor was slowed down from 650 ft/sec in helicopter mode to 450 ft/sec in compound mode, to reduce compressibility on the advancing tips.
If you wish additional information, there is quite a bit of stuff at
Sikorsky ~ S-69 (XH-59) ABC
Nick's answer to you last question will be interesting, if corporate policy allows an answer about future projects.
___________
An apology to those who dislike the phrase 'phase angle', and have actually read this far. . 
Dave