How high must a shower pan curb be?
The shower pan curb must be a minimum of 2 inches above the top of the drain.  This is common building code in the U.S.  For example, if you have a 1/4 inch per foot slope, and the curb is 3 feet from the drain, the curb must raise 1 1/4 inch from the shower floor.  Of course, this is for the finished shower.  The curb will be higher before you put in the pan.  The 6 inch figure you are finding is for the shower pan liner.  The liner should go up the shower walls at least 6 inches.