The only reason I chose to key off the four is that finding exact position on a ball close to the rail can often be tricky and especially, as in this case, you might end up father from the five (given coming from the six) than would be ideal. On any given try, I'm probably going to get better on the two using the three / four rather than the six / five. Yet, variations in the game are in part what makes it interesting.
_Rick