I absolutely agree that asking a researcher to run the evaluatory studies for designers is the optimal solution. However, even there in the briefing, designers have a tendency to sneak the justifications for the choices they’ve made and, in turn, impact the way in which the researcher asks questions. This is why I would love to propose to start by the designer looking for falsification of their design. Then they can “fuel” the questions of the researcher with this falsification — attuned mindset. Does it make sense?