You still aren't listening.
Actually I am listening, or reading, very carefully and precisely. As a result I have identified a number of factual errors throughout this topic.
You pull to your max power BEFORE you get anywhere near the OGE hover ie at the same speed you would be assessing your inaccurate Vy MAP somewhere between 6 and 8 inch power margin.
This is the first time you've written that this max power test occurs at Vy. Since that was not explicitly stated I had erroneously understood that it was part of an OGE hover test.
Instead of relying on an approximate assessment of power available, you have proved that what your charts require and what you have planned is in fact available in the conditions of the day - all while flying quite safely above ETL.
If I understand this correctly, this can be broken down into two concerns:
1. That the engine is capable of obtaining a given, indicated MP.
2. That the helicopter climbs at some vertical speed.
Your way isn't backed up by any empirical evidence or accurate power assessment - my way confirms the POH figures, provided by Robinson, are available - which do you think is more accurate and therefore safer?
With respect to (1) above, that is true. However if an engine has a problem producing power under those conditions it will be known long before then due to the way the engine is derated and the way that derating is respected by means of the MAP chart.
With respect to (2), there are no numbers in the POH that say if you can obtain a given vertical speed at max power and Vy then you can safely attain OGE hover performance at that density altitude. Thus a given vertical speed reading becomes the same sort of rule of thumb that the 6-8" of MP margin is. Both methods are empirical by definition.
Absolutely willing to be wrong here...