Over 4 years of HRT, and I doubt that mine have reached an A cup. A long time ago, I took the attitude of "Fake it till you make it". I wear small breast forms or push-up bras still, probably always will at this point.
4 years full time, happy as I can be, and my breasts are okay too. Occasionally, I think about having implants, but I really don't mind being a flat-chested girl.