So in the example you gave of Saotome shihan, he instantly incorporates you into his body map via the contact, "owns" you, so to speak, and therefore he can do what he wants? Because two bodies are now one body?
Its not that simple.... you as the attacker are doing the same thing. When I grab you, or even put my "target acquisition system" on you to strike, I am also incorporating you in my mapping system. Aiki incorporates various ways in which that gets manipulated. But yes, I think this is the origin of the phrase "ittai-ka" or single-body which the Founder talked about.