Jerome, I think this is because the Overall Story is where the “big” Problem is, the Relationship Story is where the “almost-as-big” Problem is, and audiences tend to want to know “what and who solved these Problems, and which approach made the difference?”
So the Story Guide sliders for the OS and RS are just there to help you predetermine (if you want to) how you, on an incremental scale, want the audience to feel about the focused-on Issues… which is not necessarily what your MC and IC feel on these Issues, because either or both of them could be at quite an extreme.
However, the balance of efforts and outcome presented in your story, especially in the OS and RS throughlines, may still leave your audience feeling only moderately biased on these issues, even while the MC and IC felt more strongly (perhaps to no significant advantage).
Does that make sense to ya?