I've looked into ISFp and I don't relate to it at all. I also do not think I am an Si ego for a number of reasons and I somehow get the sense that ISFp is kind of "Swiss" in his or her attitude toward things. I do not think this type's reactions to people and things are as strong and decided as mine, but that's just the sense I am getting. I also do not put on a happy face and try to ingratiate myself to people if I do not otherwise feel happy or positive about said situation or people. I can be civil, but I am not going to be nice and will more likely than not come off as cold and unengaging if I don't like someone or if I am upset. I used to have a boyfriend that would pretend to be really nice, outgoing, and engaging to everyone, only to be angry and spiteful when they were gone and this behavior is such a turn-off to me; why not be honest and at least (somewhat) represent your real self and sentiments to people?

Anyway, ISFp just sounds all around too light-hearted to fit me.