I bought a medium according to the size chart and was surprised at how the top scooped so much water through the neck so I bought a small and had the same problem. There is no extra support for running either.  I''m averge size 5''4", 125lbs with a 36C chest.  Going back to my Zoot suit for triathlons because it has the bra shelf for running and no scooping water when I swim.

I normally wear a medium or large but ordered an XL since large was out of stock and I read that it runs small.  The XL is still WAY too small.  It fits me like I would expect a small to fit.  Also, there is no shelf bra.  On the bright side, it is really cute and I wish it fit!

I'm tall and thrilled when I received the item and it's long enough but it's too tight .  I'm having to order up a size but like it enough to return and reorder