Possibly changing after every sortie might get a little weird. Maybe instead of autochanging, ask if they want to change instead?
Also I might put something in where if it's within a certain range of evenness (for example, +/- 10%) it wouldn't trigger? If it works and lots of people are using it, if a couple sides are just bouncing between being the lowest numbers it might get into a situation where it ping pongs some people back and forth every sortie.
Wiley.