Wasn't sure at first
But when i saw this top in person, urged by my stylist when they got it in, i decided to try it on. they had xs in store, my former normal size (xs or xsp). that was too big though. not being sure how the petite would look, and not sure if smaller would work, i decided to order all three: xxs, xsp and xxsp!

verdict on size: xxsp was pulling at the arm holes, kind of small there. xxs regular was almost right, but arm holes were a little high, not as comfortable.
xsp ended up being the right c