I think that I've inherited more of a Watersons style, then. If somebody else is singing a harmony close to the one I'm singing, I might well shift to another. Again my harmony will depend most on the pitch of the melody singer(s). There are some people I don't song a high harmony to, because I know I can't get higher. On the other hand, I pick up some harmonies from recordings - an example of this would be the Voice Squad's 'Parting Glass'.
But I also sang in a church choir from about age 8, and later in the Hull Youth Choir, doing all that formal oratorio stuff, so some of it might come from there. I'll be interested in Dave and Anni's workshop should it come near me - as well as being so knowledgable, they sing cracking harmonies themselves.