I'm actually a 32DDD and the 4 fit great, I could even wear a strapless bra with it. (renttherunway.com)
I immediately died when I was this print a few weeks ago, and opted to go up a size up so I could still wear a strapless bra underneath for support. (thestyledfox.com)
It's subtle enough that you can still wear a strapless bra under it and your entire back isn't exposed, but it looks great when a little bit of wind catches it! (aloprofile.com)