...when pairing up to train, folks didn't mix up very much... Is this the way it usually works in sit-by-rank dojos?
I think most yoshinkan dojo sit by rank (its considered orderly), and no, that's not the way we train, since the instructor usually calls kotite (sp) when they want the partners to change. Since we tend to train in lines, that usually means the jr. person moves to their left, and the jr. at the far end comes to the front of the line. This way, everyone trains with different people. After class training is a different animal; there, people tend to pair up based on preference more.