It is my thoughts that it is quite likely that there is lots more of what they prefer to eat in the shorter waters , they tend to feed on a much more highly variable diet than the white crappie.
Some studies have shown they consume lots of freshwater shrimp and ever larger plankton , one study I read , suggested that their stomach contents in locations east of dfw was 85% shrimp .
And we often see large black crappie take really small jigs in these parts up high in the water column as well