Re: Where's the hara?
Well, the physical center is not interesting to me. When people say move from center, they mean the second definition you were refering to. If anything, on the physical side, the center of your movement would be where your legs attach to the trunk of your body.
Can you elaborate on "sayu undo" and "Aiki-taiso"? I am not overly familiar to those terms and I suspect I have alternative terms for their concepts. Thanks!