How many different ways can someone tell you that the Mean is not by definition 50% of the Maximum? All the Mean equals is the level where the most people fall. Each SD away from the Mean makes someone more rare. There is no reason to believe that 50 MUST be the Mean.

It seemed likely for a while that 50 was the Mean because of the minimum and maximum level RJ imposed on the Bell Curve, but it's not Mathematically necessary. For instance, the Mean height for a man is roughly 70" with a SD of 3". Thus a man 3 SDs above the Mean would be 79" but would represent less than 1% of the population. likewise a man 3 SDs below the Mean would be 61" tall and represent less than 1% of the population. In neither case is the mean 50%. the only thing that MUST be true here is that there are as many SDs BELOW the Mean as ABOVE the Mean. The actual number doesn't matter as long there are an equal number of SD on each side of it. A Power scale and a % of total power are two different things.