Does the "Ergonomix" prosthesis change the shape behind the muscle?

My muscle is not so thin, I would like to put a small prosthesis 245 to 275cc mini, I have already seen several results and they satisfy me. my doctor says that when positioned behind the muscle, the prosthesis of this size will be pressed by the muscle and will look like a male pectoral prosthesis. I want a small chest 275cc MINI max! He wants to put me between 300cc and 340cc DEMI...the sizes are HUGE by comparison. Does what he says make any sense? 275 mini to 340 demi are very different.