I feel like the A cup can give you a headstart. (Though I can't tell you whether that just quickens the start of your brest growth or can result in bigger sizes eventually.) I had small A cup when starting hrt and growing started at about 2 to 3 weeks. Since then (5 months) they have grown a lot and already fill an actual A. (I should remeasure them, would be interesting how close I am to B.) They already look like a "valid" breast. And I'd be happy even if they wouldn't grow any further. (Which I think they do, but who knows how far.)
However, this may be completely unrelated to my former gynecomastia. Also, I started hrt at a relatively young age, in my late teens.
This is an interesting question thoug, which I wondered about myself before.