I tried on the xs in store, but ti was a little big on me (and i usually get petite in dresses, unless they are mini dresses).
so i decide to order the xxs petite. it fits much better. the length is, at the highest point, just above my knees. the chest part fits better on me as xxs p, the plunge is not low, not too high, and is flattering, i can wear a regular bra that can attach as t-back and you won't see anything. 
the model on the picture is what it looks like as a usual size (so xs instea