Theoretically there doesn't have to be. They're tied together already by virtue of the narrative structure.
At the Genre level with the arrangement of the Throughlines (an arrangement of four creates a "Genre")
At the Plot level with the shared location of Concerns.
At the Theme level with Catalyst, Inhibitor, Unique Abilities, and Critical Flaws.
At the Character level with shared Problems and Solutions, Focuses and Direction.
This article should help: Tying the Towers of Story Structure Together
For the same reason that the encoding of the Main Character Problem does not have to have a single thing to do with the Main Character Concern is the same reason the Influence Character Throughline doesn't have to have a single thing to do with the Main Character.
They don't even need to meet once.
It's a lot more difficult showing how one perspective is impactful and influential when it doesn't have an appreciable effect on the Main Character - but if you're effective in communicating that YOU perspective that creates conflict, then the narrative will still hold fast in the minds of the Audience. It will still work.
The storyform keeps track of all the connections - as long as you follow that you really don't need to worry about anything else.