We know all the IC story points impact and challenge the MC's perspective on their personal issues.
This is true of the IC Signposts also -- during that portion of the story the IC will influence the MC in terms of that Type (e.g. impact the MC's Future, or Subconscious desires, or whatever). And generally that impact is something that challenges the MC's perspective, pushes them toward changing their perspective.
BUT. Imagine a Steadfast-MC story, where by the fourth act the IC has gone pretty far down the path towards Change. Can that fourth IC Signpost, while still full of impact, actually strengthen the MC's steadfast resolve?
I think I'm seeing this in my own story -- my last IC Signpost turned out to be The Present, which made me laugh out loud because the biggest IC moment is when she actually becomes present in the MC's head! And though I'm a long way from writing that scene, from what I can tell her presence helps him Control things (MC Problem) and cements his Response of Feeling.
Also in The Fugitive analysis the 4th Signpost of Conceiving is illustrated as
Gerard is able to put the various clues together and comes up with the novel idea (for him at least) that Dr. Kimble may indeed be innocent.
Which is actually supporting Kimble's steadfast resolve!
I guess even the 3rd signpost might be like this if the IC changes early...?