I dunno, for IEI, I think it's more of an underlying intensity which only sticks its neck out once in awhile (at least in my case).
In any case, I'm not sure you're beta? You seem too nice or something (yeah okay I know I'm nice on the forum). but for instance, being all worried about that person enjoying themselves at a party? I have to say, I'm not like that. I would never have those questions running through my head. Maybe if they were my best friend or something but then I would already know why they were sad. Otherwise, I'd just assume they were in a bad mood and probably avoid them! I definitely don't see it as my responsibility to make sure others have fun. In other words, as sad as this probably sounds to you, I would probably abandon the party pooper rather than trying to be some "loyal friend" by pulling them in. To me, if they aren't in the mood to have fun, then they aren't and my job is to leave them alone.