Why I'm coming back for more.
Mulling it over, I feel like my answer above will just be more of the same for you. It is safe for me as a poster because it is vague and avoids specifics. However -- for you -- it doesn't solve the problem of seeing the craft that Throughlines try to explain (or inspire).
I won't let my fear of getting beat up on the forum stop me from giving you an answer that I value instead of one that protects my fragility. All information here is assumed (by myself) to be true at the time of writing. It is a good faith attempt to share my imperfect understanding. Be warned, if you come with me, "here be dragons..."
OST -- the plot as it concerns the story goal
RST -- The story as it relates to the relationship and conflict between the Main and Influence Characters
MCT -- the Character representing the audience's position in a story
ICT -- the dramatic progression which builds the Influence Character's pressure on the Main Character to change
Let's immediately get OST out of the way. I'm going to get bopped in the head for this one. I already know it in advance. Every story needs a question, an argument, and an answer. Admittedly, one could say that with the proper argument, there is only one question and only one answer possible. But there are practical reasons to at least mention that other two in passing.
Craft is necessary to blend and embellish the OST. But, at the base of it all, points of progression exist as the OST. The OST is about the movement from one to another via hitting a checklist of processes (emotional, logical, skeptical, etc.).
From the beginning, I have felt that Dramatica clears the road and shows the path for the pure emotional experience. The OST is about quieting the skepticism of the mind and allowing for the heart to enjoy a bit of catharsis.
MR Units and Dwight Swain (Don't Be Dismayed)
Though I might hear a collective groan, I want to reference Swain again. He talks about the MRU (motivation/reaction units) in his lovely little tome. The MRU has two parts:
Motivation Units (MU) are described by Swain as Objective. That's a simplification. And I feel Swain knows that it is a simplification. However, he doesn't want to throw writers into the deep end immediately. And I feel like Dramatica is the deep end.
Reaction Units (RU) can be described as the Subjective. That's a simplification. And I feel like Swain knows that too. Once again, he is trying to let you come to a conclusion without telling you the conclusion you should come to.
Well, how are those statements simplifications?
Because both of those units can contain the MCT, ICT, or RST which would seem to be conflicted by his use of the terms POV. But somewhere in that nifty tome of Swain -- he mentions that objectivity is a hairy concept. And he also mentions that rules are great for bending and breaking (that's paraphrasing at its finest).
What can you do with the Motivation Unit that is supposedly objective?
Create comparisons/contrasts/parallels of the environment and character via specific imagery or active setting (MC Throughline, IC Throughline)
Create comparisons/contrasts/parallels of the environment and relationships via specific imagery, active setting, medium (RST)
Create emotion, mood, and tone for the MC, IC, Relationship via specific imagery, active setting, and medium (MCT, ICT, RST)
Specific imagery is important because the connotations involved. A Doberman draws a very different emotional response from us in comparison to a poodle.
Active setting gives a sense of motion, but it can also give a mood by contrasts, comparisons, and parallels in regards to the emotion, moods, and tones of verbs. It comes down to connotations again.
Objectivity is anything but objective. As a filmmaking, when you frame a shot, you look at everything in that frame and you decide if it is relevant to the scene. You will hardly see chaos in a frame unless chaos is useful to your story. Because chaos is distracting... unless you want to distract. On the other hand, order can be distracting as well... unless you plan on distracting with order. There's always a balance.
In reference to the RST, Swain touches on it in passing I think. He mentions something called a WEENIE or BONE OF CONTENTION:
The paper clip lay on the desk between them. It was an old clip-discolored, somewhat bent, with a couple of small rust spots visible upon it.
Idly, Olivas reached for it.
In a voice dangerously gentle, Sheehan said, “Touch it, you son of a bitch, and I’ll cut your throat.”
Olivas’ hand stopped.
You see? Itself unimportant, perhaps, the paper clip is a symbol of the relationship between these men. Their reaction to it and to each other bring a host of elements into focus—the state of mind of each; their caliber and potential; all sorts of things. So, whether the paper clip itself is intrinsically of worth or consequence or not—and it quite possibly may be—it serves here primarily as a bone of contention between these two.
Does this paragraph talk about the individual characters? Yeah. But it is about the relationship. That short scene gives life to the CHARACTER that is the RST. I think you can use the term CHARACTER if you are willing to expand your definition of the word. The relationship is the character. You can use character to describe your scope of focus. POV (as it seems to be used) is about scope... not about who is looking. The audience is always who is looking, but what skin and what direction and vantage point are they looking from?
Imagine if you always saw your friend Tom and David together. For five years, you saw them together every time you saw them. Then, one day, you saw Tom. Where's David? It's like seeing half a person. Because the RELATIONSHIP has a life of its own.
Also, I think that most RST can be shown or told. People are always saying that crap all the time. Show! Don't tell! Well, I like to look it as the craftiness of hiding the Omniscient POV. I disagree with the idea that Omniscient POV has been somehow removed from most modern novels. It's become subtle. The author is talking to you ALL THE TIME. He is bonking you over the head. But he doesn't want you to know he is bonking you over the head into submission to his argument. I'd say the Omniscient POV is the GAS.
Dramatica is like that to me. I'm tapping away my point. I'm just doing it in slightly different way the entire time. So it doesn't feel like I'm hammering. It is more like subtle waves of urging someone to an answer.
What about the Reaction Unit? That's just the MC right?
The RU provides us a very obvious outlet to express the MCT. As mentioned before, we can augment it and reinforce it with the MU through comparison, parallels, mood, tone, etc. Maybe the MCT is about vicarious emotion, the ICT is about witnessed emotion, the RST is about a witnessed emotional ecosystem.
My Short(er) Answer
I think that statement of "these are not characters" applies primarily to the RST and OST. The OST is our path through the Story with no embellishment other than broad strokes. The OST characters are only valuable in terms of how they are similar or related in the expression of the Storymind.
The RST cannot be about the MC or IC (characters) because they are already represented. It must be about something else. A third unnamed character (if you expand your definition).
I also feel like RST must be subtle and subtextual unless you want to blatantly use Omniscient POV or make some of your characters gossipy. I seem to recall an example that was given in one of the posts around here that illustrated two other characters yammering about the relationship between two people. And that was an example of exploring the RST. One of very specific usage I think... and one that could become tiresome really fast. Half the battle is still about understanding the craft too I think.
I'm feeling bold. I'm going add... I see OST, RST, ICT, and even MC as what we are looking at. But I see MC as fulfilling where we are looking from as well. MC is the only one that we look from (unless we break the rule and we surrogate for a specific reason). Other than the hidden GAS/Omniscient POV.
In a novel, we have to cheat to see the world through the eyes of someone other than the MC. But cheating is fine. At times. For certain effects.