The Domain assignment must be different for each of the viewpoints within the same story. In that way, all points of view are covered as well as all the classes (domains).
When you write a "Grand Argument Story," you need to cover all of the relevant story points to make a convincing argument to your audience. You do this by establishing some points of reference and then exploring the story problem(s) thoroughly. If you leave something out, the story will have holes. If you neglect to set up your givens, the argument of the story will fall apart if used out of context. In both cases, your audience has the opportunity to dismiss your story because of faulty structure. Assigning the four throughline perspectives (MC, IC, RS, OS) to the four structural "classes" (Situation, Activity, Fixed Attitude, Manipulation) establishes the story's points of reference while encompassing the potential sources of the story's problem(s) and corresponding solution(s).