Well, lets see, symantics 101. To me, presence describes the effect the dog has on the stock, where power describes the dogs ability to do work (sorry, the physicist came out). In answer to your question about presence and no power, I think my male qualifies. Everytime he steps thru the gate the sheep seem to say "I'm out'a here!" and scatter, he doesn't have to be anywhere near them. As you can imagine, getting any work done with him is nigh on impossible. My female on the otherhand is just about the opposite. When she comes thru the gate, all the sheep look at her, as she gets closer they flock together, wherever she directs, the sheep go. Needless to say, most of the work gets done by Bet. I'd say you can have pressence without power, but not power without presence.
Dave