I think when one looks at a characters size. They should consider things like the camera angle and other charters relative heights.
For example the reason Gecko Moria looked so gigantic in his first appearance was because of both the camera angle as well as the people who woke him up were a bunch of midgets.
Heh all this talk about height reminds why I want to see the BB Pirates get some Girl members. I find the concept of a attractive and not too manly looking woman being 8-10 feet tall extremely hilarious.