I’d still say that, socionics-wise, this is mostly an intertype relation thing.

But I mean, getting to know someone involves cracking the shell around their idea of self and peering inside, right? So again, socionics-wise, I think people would mostly put stock into their base function and creative function as their sense of identity. So I don’t see why Fe PoLR would principally make someone harder to get to know as some people seem to suggest. As far as social gregariousness/withdrawnness goes, I think we would be better off leaving that to something like Big 5, right?

So I emphasize my stance on this being an IR thing, but to really squeeze an answer out I would hesitantly say
IEI

Because:
• Despite what I said about Big 5, it is certainly true that introverts are generally more socially reserved all-round
• Ni is regarded as a more (the most I think) nebulous function and thus is more difficult to effectively grasp
• And I considered Reinin dichotomies yielding/obstinate and asking/declaring to be most pertinent to this.
I think yielding and asking would be more deflective and IEI has both.

Hopefully I am not showing too much weak Ti/Te skin... I try to be a modest boy...