The reason I use height as a guideline and not weight or position is because, in my opinion, the dominant factor is length of the stick. The longer the stick, the greater the amount of torque you can put on it.
Let's take two players. Say they have equal strength, in that they can both bench, squat, curl, whatever measure you want, the same amount of weight.
Their body weight is irrelevant. There are guys who are 150 pounds and can bench 200 just like there are guys who are 250 pounds who can bench 200.
That 5'6 player will be using a stick roughly 6" shorter than the 6' player. Chop off 6" of stick and you're increasing the flex roughly 20-30 percent (per Bauer's guidelines). The short player would have to put 20-30% more effort/force into the stick to achieve the same deflection.
So those heights are a starting point, just to get everyone on equal footing. It's nice to try other flexes but usually you'll land in that range.
I remember doing a poll over at Mod Squad and gathering 100 responses or so looking at height and weight and flex and there was a pretty solid correlation between height and stick flex. There's also a correlation between weight and flex but only because there's a correlation between weight and height. Especially when you're looking at scrawny teens and schlubby beer leaguers like me
