All the checkrides that I have assessed have been in the aircraft itself, where one can only go so far in allowing a dangerous situation to develop. At the debrief, it is important to make the point that intervention was necessary (either verbal or physical), which reduces the posibility of 'pushback' from the examinee.
I think that the most interesting aspect of this thread is not the means by which you convey that the standard has not been achieved, but the attempt to discover why it has happened, especially with experienced pilots. It is extremely rare that a lack of natural aptitude is the cause, except in the case of student pilots. I have seen cases personal pressures, chronic fatigue, simple lack of motivation and in the extreme, potentially severe medical and psychological conditions. Nearly all can be salvaged, and if possible, I have tried to the focus the debrief in that direction.
Apologies for the diversion!
Mel