I don't think this is exactly accurate.
I still think the clearest way understand what's going on here is to use the initial Dramatica terminology/delineations. This terminology is in many cases borrowed from more conventional understandings and redefined by Dramatica for more specific meanings. Many of us may be a little sloppy in how we use the terms in discussions on the board, which could cause confusion.
So just for clarity, here is how I understand the Dramatica model and terminology as it relates to what I think you're asking (sorry for the length and if any of this seems obvious or self-evident):
Stories have players. These are what are conventionally known as "characters." From a storytelling perspective, these are the individuals who have biographies, likes and dislikes, talents, a certain physical appearance, etc. These characteristics are separate from structure.
From a dramatic structural perspective, these players play different roles (take on different perspectives).
This is where we get the four throughlines.
The OS throughline (the "they" perspective) is where you find all of the character Elements in that window of Dramatica. Different characters will play out (explore) these Elements over the course of a story. Archetypal characters take certain conventional assemblies; complex characters mix and match. The most important of these is the player representing Pursue -- who pursues the story goal. By Dramatica convention, this player is called the Protagonist.
Then you have the Main Character (I perspective). By convention, most stories combine the MC and OS Protagonist into one player (e.g. Luke Skywalker in the first Star Wars movie). However, there are many stories that don't do this -- the Protagonist and the MC are represented by different players (e.g. To Kill a Mockingbird.) The important thing is that in Dramatica, the Protagonist and the MC play completely separate dramatic functions, even if they are portrayed in the same player.
The Influence Character (the "you" perspective) who challenges the MC can be represented by any number of players. Often it's the love interest. Sometimes its the OS Antagonist. Sometimes it's the guardian. Sometimes its the OS Protagonist. It really varies.
The Relationship Story is, again, it's own thing. By storytelling convention, the players in the RS are almost always the same players who take on the MC and IC role. But, just as the Protagonist and the MC are only the same in the sense that storytelling convention usually puts them in the same player, it technically makes no sense to say "the actions of the MC and IC reflect the state of the RS" because the MC and IC perspectives are completely different things from the RS.
More accurate I think is to say: the players in the RS express and/or reflect (expose?) the state and progress of the RS. Most commonly, these are the same players who represent the MC and IC perspectives in those respective throughlines.
The idea that these are all completely separate is where you get Hunter's experiment in creating four throughlines with completely different players. Theoretically, this is structurally perfectly fine, though it's very unconventional and might be hard to pull off, and audiences might be confused by it (but it could also be super-cool...)