Yes, everyone develops differently and what size you get is really luck of the draw... It's the same with cis women, some get a BA, others are rather proud of their lil' boobies
I knew a girl that worked in a bikini shop who was very depressed about her A cup breasts... She saved her money, took some time off and then one day she showed up with a rather perky pair of C cups
Back in the early 90's when I was working as a chauffeur and long before the movie* came out, I drove a group of gals from the ITTY BITTY TITTY COMMITTEE club... They were wonderful, attractive and vibrant women who were proud... And they gave me an incredibly awesome tip when I dropped them off

I don't know, maybe give the HRT a bit more time while you explore your options?
*
http://en.wikipedia.org/wiki/Itty_Bitty_Titty_Committee