As I said rachel, most TS underestimate how much pectoral they had.
If you had little muscle, you'd look weird. I've seen MTF with little
muscles and they looked very week as men, but now with
breast tissue in the right place, they are better balanced.
That's why I smile when many TS say they are B's in 4 months, yeah
they fit a B cup, but much of this muscle that will go away and fat
that shouldn't be there. Many TS are overweight before they start HRT
because of self-esteem issues. Later, pects will diminish and your chest size
actualy will actually decrease while keeping the same cup size (what could
cause this but muscle loss...).
If your band size goes down a lot, its because of loss of fat and muscles.
Women who are overweight need big band sizes.
If you lose fat elsewhere (you don't need to be obese for that)
your breast can go down in size substantially, depends on how much
of it is gland and how much is fat.
I lost 30 pounds and even if you saw me before, you'd not
say I had that much to lose (though part of this weight was muscles, but most was fat).