On a side note, my Sensei has been out of the country for a few weeks and various senior students have been teaching in her place.
It has been a variety of Sempai with even a few 1st kyu. I have learned equally well from all of them with some having strengths in teaching based on their personality, experience in teaching, and expression of their own learning process.
Here is an article form this site that explains some.
http://www.aikiweb.com/teaching/rock3.html