the ring of water can perfectly be placed between the boxes and the central tower on this picture.
http://www.batoto.net/read/_/212590/one-piece_ch732_by_powermanga/18
Oh my bad I see it now. I think it's like an optical illusion. The tower looks like it is much closer, but it's really just huge. Otherwise yeah those toys would be huge and the tower small. Though I still think there is something wrong with the scale, given how big those boats are. Even if the tower is huge, I say it should still be smaller that far away to give more room to fit these moats.