Why are Signposts sometimes explored with Variations from other Domains?

The Plot Sequence Report gives us the Variations to be explored for each Signpost. But those Variations sometimes don’t belong to the Domain for that Throughline.

As an example, my MC’s domain is Situation, with a Signpost order of Present, Past, Progress, Future. Yet, for each signpost, I’m to explore the Variations under the Fixed Attitude Class…

My OS is Physics, yet its Signposts are explored using Variations from Situation.

MY IC is Fixed Attitude, yet his SIgnposts are explored using Variations from Physics.

My RS on the other hand, is Psychology, and is explored using the Variations from its own Domain.

I suppose it’s different for every Storyform.

But I’m curious as to why this happens, and what it means about a particular Throughline when its Signposts are explored using Variations from another Domain.

To be clear, I’m not asking about anything proprietary here. Just curious about the “why” and “what it means” aspects of this.

“An ‘inside’ view of the storyform—what the world would look like from INSIDE the story—would look much more like the Plot Sequence Report describes, where there’s a whole lot of mixing up going on. That is a completely valid point of view, but seems to hold little bearing to the ‘outside’ point of view represented by the Dramatica story engine settings and story points. The Plot Sequence report is the one report in the Dramatica Pro software that gives you an idea of what that world looks like from inside the story.”

You can read more here: http://dramatica.com/questions/how-do-i-make-sense-of-the-plot-sequence-report