I have an L size. After consulting with Alpha rep, I've ordered the size. However, it sits just tight on my body (though shoulders are okay). It doesn't cover my butt and it's very important for Moscow's freezing winters.
Also, it is way far not warm as it looks like. It's okay to 0F. You need thick wool or fleece layer to wear with N-3B in colder days.
Buttons fell off in a couple of weeks. Had my GF to put it back.
Doesn't worth its money.