(Made by BlackCat. Take it with a grain of salt, if you wish. However, in theory, I don't think it's hard to grasp how Ni may play a part in inducing the same kind of anxieties 6's must cope with. How the other functions of an INFJ, in particular, converge with 6 tendencies seems more open to interpretation.)
Yes, I recognize that Si often functions as a repository for symbolic information.
And while I think Will frequently makes decisions as an INFP would, he suffers from so much dissociation (off and on the job) that it's hard for him not to look like a Pi dom. Sure, he searches for himself as an INFP would, but I think the typical INFP has the puzzling tendency to simultaneously show a robust sense of self. Or at least
attempt to, in whatever fashion they see as most fitting, sometimes regardless of how truthful it is. But the most I see of that in Will is by way of his principles. Principles I could see as byproducts of Ti.
We also see Will drawing conclusions with very little information on hand (even when he's not in his "zone"). Are we to say his offhand insights stem from Si as well? His years of education and training?
In any case, I interpreted Will's hesitation to kill Hannibal not just being motivated by his desire to understand himself, but also to apprehend Hannibal in the most honorable way possible. Do you still see INFPs as that self serving, that they would let a killer go just for the sake of personal introspection?