Post process volume priority

Hello, I would like to understand the Priority Number in the Post Process Volume. I have two volume. A big one and a smaller one inside. I set the Priority of the outer volume to 1 and set the value of the smaller volume to 2. I expected the inner Volume to overwrite the Volume with the lower number but actually the result is a mix of the color settings from both volumes (Blend Radius = 0, Blend Weight = 1). Is there a way to suppress the first volume on entering the volume with the higher priority? And by the way, in which situation is this mixing behavior helpfull?