I have gotten warned while 3 feet ahead of the next player, so sensitivity may be a bit off. Also a lot of chat messages and the warning announcement is a little distracting, especially in the fake announcements era of the game.
I think your math might be better served by referencing the person farthest back and then looking at some fixed distance ahead of them before generating a rushing message, the average thing gets thrown off if there are 1 or 2 frontrunners with a peleton behind them.