I fully agree with you. With "This type of airplane does not have a clear stall" I mean that the airplane doesn't pitch down abruptly like we are used from other single engine airplanes. This one just drops the nose slightly and it enters into a kind of a "nodding" (pitch oscillation) motion. Therefore the "The control reaches the stop" will be the determining factor for the stall speed.
There is still the question for the correct maneuver. During our investigation the question about the trim condition came up. The regulation states that the airplane has to be trimmed at 1.5 Vs. Does that mean that the airplane has to be trimmed in power idle which would result in a descent or in power for level flight at 1.5 Vs and than the power will be reduced from there before the stall maneuver?