In my oppinion Yamato look smaller because the bra that she wear made from metal and it surpress her breast while Iowa doesn't wear ant bra, I'm not gonna talking about historical reference though I'm just want to pint that out from character design reference it just my oppinion though
Actually, her CG shows that she has two turrets on the right and one on the left. Here, the turret on the left is obscured by Yamato's own turrets.
Negatory. Iowa's turrets can rotate on their armatures so that they are all lined up on one side. That is how it is in this image and her damage sprite. The rear/left turret is in the upper left, and her right hand superfiring turrets are in the lower left, though only the range finder and top of the forward-most turret is visible.
I have a theory that poor Yoshinori is somewhat proud of this clever design, but no one really picks up on it. So he made it a feature of this image. (But it's still easy to miss...)