Figure out how different bw auth positions actually affect the measured bw values

We believe that bw auths are concentrating too much bandwidth in one area (see: team#179 (closed)). However, it's not clear how exactly different bw auth positions affect the measured bw values. It would be useful if we had some means to investigate that question and then (in a follow-up ticket or so) come up with a better bw measurement plan tuned for our network.

/cc @juga, @mikeperry