While I was trying a kote-gaeshi, he explained (Rob translated) that he was directing my pressure to his center through some lines, although I can't say I actually understand the meaning of "inside lines", "outside lines", etc.
Heh, this is one of the "secrets". As you develop internal connection/ lines/ tensions, you'll learn that when one part of your body is moved, you can (literally) feel a pull in other parts of your body.
As you continue working on Ark's exercises, every now and again have someone put a kote-gaeshi/ nikkyo/ etc on you (or practice the locks on yourself). Have them apply pressure real slow and gentle, so you feel more of a stretch than a lock. Stay real relaxed and pay attention to how it feels. Where do you feel the stretch? How far can you extend
that stretch? Can you feel it in your forearms? What about your upper arms? What about your body?
When you get to the point where you can feel the stretch in your body, you'll really be able to start resisting the pressure like Ark did. (At least, that's what was been told to me, I'm not there yet.) Part of this is a mind trick, but a lot of it is simply developing those internal lines/ connections/ tensions.