I would up the blueberries to 3 cups and add an extra 1T of flour to the Sugar/Flour/Zest mixture that is added to the blueberries to sweeten and thicken them. This would give complete blueberry coverage to the bar and add more blueberry taste as well.
Whole-Wheat Blueberry Bars
From EatingWell: July/August 1995
These delicious blueberry treats feature moist fruit filling with a crunchy topping made with the same dough as the crust.
7 Reviews for Whole-Wheat Blueberry Bars
This is what we found. Far too sweet. So the next time it was made we halved the sugar in the crust. 1/2 cup is more than sufficient. We also substituted honey when we cooked the blueberry mixture. But it offered a wonderful starting point.