*looking back at the manga* Yes, while maybe there was some bagginess in their school uniform, in the first Volume of Railgun, Uiharu and Saten both look basically flat, even compared to Misaka.
Even in volume 6, in the manga, she looks flat, but then, when I look at the cover art for one of the chapters, which seems to be an ad for the anime version, she's in a bathing suit while being fairly well endowed.
I guess she started out flat, but fans have been throwing in more and more padding, and some of the promo stuff or anime is gradually inflating her bra size... (Or maybe she's just having a growth spurt?)
