I think that it is really rather normal that people who know you have a harder time "getting it" than people who dont know you at all. Meaning that you can "pass" to strangers but not to people you know already in the past - for them it is more a matter of changing their own view about you. And I think most of us know how hard this is even for ourselves. I believe that few of us here did not have the experience of looking into the mirror and seeing a face that reminds oneself about a person of the "old" gender - ones own brother or something - basically this is "not passing" to oneself. I guess with FFS and such, this can actually be thwarted, but without that, facial features can always remind one of the past - even more than what other people would notice. This is the same with friends - they dont look neutrally at you, just as yourself dont do it - instead they look at the face and recognize a person they know and then it does not matter if that face changed in some ways, but the identity assigned to that person comes from the memory, while strangers will take a more neutral look at your new self and identify it with your new appearance and your person and gender as it is and thus have less issues with that cumbersome memory of the "old you".
I had the fun once and went to a school reunion. Didnt see the people for about 10 years and was about 2 years into transition, HRT and all. A few people identified me and they had some trouble getting the name right and all that after I told them. Others just didnt get it, they kept saying that I seem familar but they cannot remember really who I am - until they were told by someone who I was, they did not really have an issue withnames and gendering, but afterwards as memory set in, they suddenly had. Its all about that memory.
Zumba, I think your path is a very good and admirable one, but I also think that it is easier said than done. Being post-op for over a decade myself now, I think in part this is right - one learns a lot in these years, but at least I myself have still much more to learn as I am not the most sociable person that gets into friends circles easily. What I think is rather hard is to get to that acceptance for myself. To have the confidence that everyone will see you as a woman, that you are free to do whatever you want and still feel and be perceived as a woman, that is sort of the high goal and I for myself still catch me thinking that some action, behaviour or look on my side is too male or that if I do this or that I will be perceived as male. This leads me to being insecure. I tried this acceptance of "I am a woman but also a transperson" and to not worry about some people seeing that, but in the end it came out as a game of pretense. I lied to myself about not caring about this. In fact everytime I did something I felt was too "male" and especially every time I feel like I am not "passing", I feel really bad, try to push away that thought, pretend I do not care, but inside I feel scared and stiffen up (which de facto increases the danger of "not passing"). Normally I tend to think that people will either see me as just a woman or "read" me in that I am a woman with a trans past. But very occasionally I actually am gendered the wrong way and this really sucks then. Had it happen last month when I was in a group doing a thing where one tells a story about oneself and the other refelcts on that story. I told my story and the other guy retold my story but kept saying that "he" did this and "the man" did that. I told him later that this confused me and he apologized, but it left me thinking for days and actually was part of what led me to taking another look at voice lessons and then finally to join this forum because I really did not expect to "fail" like that after 15 years of living in my true gender.
I dont know - true acceptance to be trans and true acceptance that there will be some people who will know even if it was not told to them (and yes, i would tell a person I want to seriously have a long term relationship with) - that is harder done than said. I suspect that in part one has to find a way to accept onself as the gender one truely is - a sentence that already shows how it should be - "the gender one truely is" - in my case this would mean to really honestly and down to the soft inner soul of myself accept and know that I am female and not have those nagging doubts about his or that trait being male or worry about giving off "male vibes" as a reason for being "read" and all that crap. The confidence from being really in ones female self center I can imagine would be a great basis for not worrying too much about passing anymore. On the other hand not to worry about passing anymore because it always works would greatly contribute to reaching that calmness and security about ones identity, which I think is why so many people go for FFS and all that stuff, so that they dont ever have to worry about this again and can feel safe and secure in opening up their own inner identity and not have it harmed by stupid occurences.
I hope I make sense - please tell me if I am talking nonsense to you, english is not my native language and I am sometimes not sure when I start rambling or philosophizing if it still makes sense to others