If we’re talking about Storymind perspectives rather than a players specific within-the-story point of view, then the idea is that the story itself is looking at the IC to see how “you” see the problem, justify the problem, and deal with the problem in order to see if “I” should adopt that position.
If the MC problem is ‘everyone has a bad attitude about me’ then before the MC switches from Mind to Universe, it would make sense that the Storymind would look at how adopting the position of Universe will influence everyone by first looking at ‘you’ influence everyone’s Universe. The non-MC players that the IC is influencing would just be IC characters at the time the IC is influencing them. That they are also players in the OS throughline shouldn’t matter. After all, they’re also already players in the MC story in this example.
Another way to look at it would be that each character the IC is influencing is another fill in for the MC as they decide whether they should change or not. If the IC influences Frank and things work out for a bit and then fall apart For Frank, and the IC influences Jane and things immediately fall apart for Jane, and then the IC influences Pat and things really seem to have worked out well for Pat, then how will things work out for me if I change? To the Storymind wondering this, Frank, Jane, and Pat are stand in MC players within the IC story. If the IC character is an analogy for me were I to view the problem that way, then Frank, Jane, and Pat are analogies for the process of me changing to adopt that new perspective. Kind of like saying “if I had started out viewing the problem that way it might be fine, but now that I’ve started this way, switching to that way will work out for a bit and then fail (Frank), fail immediately (Jane), or work out forever (Pat). By seeing what happens when they change, the Storymind is essentially wondering what would happen if it changed before it actually changes. Again, that these players also inhabit the OS is of no consequence structurally.
My point is that as a perspective everything ‘you’ do should be seen in terms of an analogy for ‘this is why I should adopt that position’ and the IC player influencing others can work to do that in multiple ways. So the IC doesn’t have to influence anyone other than MC, but in the way that I view the IC, the IC influencing others jives just fine.