The amount of sugar that goes in with the peaches always depends on the sweetness/ ripeness of the fruit. If you have peaches that are super ripe and super sweet you want to add only enough sugar to help release juices and cook everything down. The same goes with the flour. 1/2 cup of flour is great for really juicy peaches, but If you're baking with not-so-ripe fruit you may end up with too dry a filling. (in the case of dryer fruit, more sugar to add sweetness and less flour, because you don't want the flour to overpower the flavor of the fruit)