Great post mars.
I am not really sure what your confusion is here outwest, but I think you are asking if the call should be made when able to fly away Vs when you are no longer considering a reject. I am with mars, the call should be made only when there is no longer room to reject on an open area, even though you may have attained flyaway speeds (Vstayup) alot earlier and I remember a detailed thread on this very question before.
I think terminology is often an obstacle to understanding or clearly communicating the situation, and "flyaway" is one such term (right up there with CDP which I was pleased to see Mars avoid). I suggest "committed" as a substitute for flyaway, followed by what you are committed to. This term can be used in both PC1 cat A and PC2 Cat B ops and allows clear and decisive communications of intent to the crew.
For example, on the CAT A helideck departures, "Committed" would be lowering the nose. On the onshore runway departure, it would be "committed to flyaway" when passing the point at which a rejected landing is no longer possible. On the CatB stuff, you use it very similarly, but in a more complex fashion. Lets say you are coming off a hospital rooftop Cat B with a nice big oval across the road from the hospital. As you get sufficient hieght to clear the roof, you lower the nose and call "committed to the oval". As you trade altitude for airspeed and attain Vstayup with little chance of a succesful reject into the oval, then you call "committed to flyaway". Clarity is the goal.
The term can then also be applied to the landing phase as easily, which flyaway cannot. The call at LDP can be "committed" to indicate committed to land, or lets say in the hospital helipad scenario, you can call committed to the oval first, and then when you are low enough and close enough to the pad to safely land, call c"ommitted to the pad."
The good thing is it is decisive, unambiguous, and can be used as a standard phrase during both TO and Landing.