We’ve talked before about what a difference a tent dress makes for a woman’s figure, as in totally obscures it. Since we’re pretty used to seeing Sienna Miller in floaty frocks, we didn’t think much of it when she arrived at the Late Show in a babydoll gray dress from her new line Twenty8Twelve. But our jaws dropped when she emerged from taping the show in a second-skin black Calvin Klein sheath dress and sexy high heels — va-va-voom! Who knew that body was hiding under all those layers? We totally relate to Sienna’s love of loose dresses, but we can’t help but wonder if she shouldn’t give them a break. Tell us: Which dress do you like better on Sienna? Should she stick to form-fitting dresses?