I don't know what the answer is, but with everything I've seen there is no rhyme or reason. Many of the fish in the park run small, maybe I should say real small, but the same is true of Taney and it's a different hatchery. In Taney some run to a nice size 12+, some in Bennett run 12+ and I happen to be at the river when they truck pulled up this fall. I would guesstimate that the fish from the truck averaged 13" or better. About half the fish hung around the ramp for about 30 minutes and thought it was feeding time in the concrete creek. I caught one 16" and most were bigger than 13".
I think the hatchery might be making it more like natural, some big, some little, just like being on a natural stream. Of course having people on either side and as far as the eye can see doesn't take away from the mystic some.