Dana,
Great post and it generated lots of wonderful responses. But I think passing and blending are very different things. Are those differences important? I don't really think so and that is because I pose the question of what does it take for a woman to pass? The point is that perhaps passing is some idealistic image of what a woman looks like. I have seen some women, middle aged and older, that I have to look at for awhile to tell what sex they are. And the same goes for some men, especially younger men. To me, passing is the ideal to shoot for but blending is the practical goal. Among the TS folks I know, only one fully passes and she admits it took over $100,000 to reach that state. Heather's behavior is fully feminine and her looks follows suit. But she admits that she has two tells - sneeze and cough. Very masculine. She has never found a way to change those. The other person, Sylvia, transitioned 50 years ago and now in her late 60's looks like a lot of other women in their 60's, i.e., a bit masculine. For the GG's it is a loss of female hormone support; for Sylvia it is induced female hormone support and more than a little practice.

I think what you have found and what the others have added and commented are all really good thoughts and are applicable almost universally. But I also think passing is some kind of ideal that is really difficult to define and may not really be definable in a universal sense. So, I think the rule should be - Do the best you can, keep your personal ideal in mind, shoot for it, but accept that it is likely you will never achieve it simply because you have an X and a Y chromosome and they have two Xs. You are male and they are female. That sets a boundary that is impossible to cross. But as Heather showed you can come awful close. Sylvia though is a more practical solution. Both are beautiful and acceptably women.