I think Raging is correct in the sense of me rarely venturing to give an opinion unless I feel like I could reasonably answer the objections that others might have to it. I would prefer not to be seen as arbitrarily and emotionally taking up a position without having thought it out (and I think many make that assumption about NFs). I think it is a form of self-protection as I want to share my thoughts, but still have difficulty dealing with rejection if I talk about something that matters to me or that is a strongly held belief. I don't think that I am trying to impersonate another type though.
I have been doing some thinking about the fact that I could come across as either stubborn, closed-minded or overly dogmatic and serious to people though. Most people are unlikely to see my sense of humour, or me teasing them unless I am quite comfortable with them and know how it will be taken, and even then it is more often shown in private. I know that some NTs are a little suspicious of me looking for common ground rather than for points of difference when discussing something. That may be Fe related I would guess.