Batter Box Position Relative to Pitch Speed

Question
My daughters are playing 13U fastpitch softball and I have a general question concerning the position of the batter in relation to the pitcher's throwing speed.  Should the batter move up or back in the box for a faster pitcher?  And, why?

Answer
I doesn't matter.  If they can't hit a fast pitcher, moving back in the box doesn't significantly increase reaction time.

Look at is this way, moving back in the box might give them an extra 2 feet.  Lets assume the pitcher releases the ball four feet in front of the pitching plate and throws 55mph.  The extra time gained in the extra two feet is almost too small to measure.  Addtionally the ball may no longer be hittable even though it was a strike when it crossed the plate.

The only time I would move a batter up in the box is to help hit a breaking pitch before it breaks.  You still run the risk of the ball not being hittable but falling in for a strike.