I do think that a lot of us are coaught between the gender poles. Other than the external parts, there's no physical or psychological reason that we might not develop at any point in between. I'd rather not get bogged down in debates about who is what, but I do think that its possible to be somewhat more towards the TS end of the spectrum, to need and immensely enjoy expressing your femininity and still retain some aspects of a "normal guy".
You nailed it by saying you've found self acceptance. At the point of self acceptance, "why" doesn't matter so much. It just is.
I remain curious about why, but only in the academic sense. I doubt that anyone will soon offer a definitive clinical test that will tell me why I am as I am. At best, there may be a range of possible explanations...and I can choose one if it suits me.