I was either a 36D or DD when I started binding. I wore a large underworks 997 double front. Got me pretty flat and I was able to semi-pass back then (pre-T). My chest would uniboob at times because I didn't know to push down and out.
As time went by, the binding broke down some of my tissues and it was easier to bind. With T, things became even easier and I looked practically flat. This was after 6ish years of binding and 1-2 years on T.