I have the same problem with people knowing me, and I'm dumbfounded sometimes because I feel like I'm actually pretty expressive and open. I have the problem where people latch on with the "It's like you and I have this...connection" and in my head I'm like "Uhhhh, we DO?". Meanwhile, we have next to nothing in common save a couple of similar life experiences.
I'm not sure why people constantly fail to know me very well. For example, I am a writer and it's my passion, I talk about this passion, I express my devotion to it and my dreams surrounding it but very, very rarely does anyone seem to take interest in this part of me. I find that people usually hone directly in on the things that I like that they do too, and since they like them very much they assume I feel exactly the same, even though all I might have said was "Yeah, that band/movie/artwork is really good!".
I also think perhaps it has something to do with HOW I express myself. I'm pretty straightforward and tend to paint complete pictures that include a beginning, middle, and end (resolution). I think perhaps it comes off like it's so resolved and I've made up my mind about it, so it requires no further attention or consideration, if that makes any kind of sense. I am also crap at asking for help or advice since I think so much and people rarely have things to tell me that I haven't thought of already, so I guess I forge some distance myself in that respect.
When it comes to people latching on to me, I think it might just be that I have a knack for bouncing back what someone has told me in the context of THEIR own point of view, insomuch that they mistake it for being MY point of view. I don't mean to do it, I try to choose words carefully by saying "So it's like you feel ________" or "So for you, it is like ______" but it stills seems to be mistaken for "OMG! You and I are SO ALIKE!!". I am also keenly aware of letting people know I am genuinely interested in what they're saying, that I'm listening and hence I validate them and for some I think this has some kind of narcotic effect, lol. Then they come back for more and more. I've had a lot of bad relationships where I did not exist outside of being a vessel for the other person's self validation and it was not good times.
I'm still trying to eek out ways to connect with folks better while still being able to exist as a person unto myself, but it's hard as I am so apt to take journeys into the heads of others to see what is there.