Shimikaze must really be conscious of her silhouette of she's jealous of Ayanami, because Aya doesn't even have much to begin with.
If you look closely at her refit art, Ayanami has a bit of a bust, given that you see underboob, which isn't something you'd see if she were completely flat. Shimakaze's jealousy is understandable, even if there's far bustier ships in both games.
A picture(?) of Shimakaze and Ayanami looking like sisters...Shaddap.It's tight around the chest, yes.