Choose people who are the same person in the group as they are one on one.

A sizeable gap between those two versions is worth taking seriously. Everybody adjusts a little depending on the room, but somebody who is warm alone and cold in front of others has decided your friendship is not for public use. The reverse is its own problem, where the private version is the unkind one. Consistency is not a personality trait so much as a measure of how much managing the person is doing.

Watch the switch rather than the single setting. Notice how a friend talks to you when the group arrives, and notice what you do yourself when somebody you like is near people you want to impress.