A stated situation is that blueberries will rise, or move freely. Thus, they do not block, do not form a body, a wall. Basil leaves are different, obstructing the body of the bread to be freely moved by the heat. This seems to have prevented the wanted fluffiness.
Lesson learned!
Just like in the case of steeping tea properly, leaves need to be free to move.
Sila Blume 