I believe you. I am a science guy, so I am always a skeptic and verify everything I can. Trust, but verified. I am assuming your measurements are correct which is why I'd like
@Precogvision to give us his take on what is going on once confirmed. My theory is that the scoop out is happening in the presence region of the curve and where sibilance is most common. So, What the scoop out might be doing is allowing us to listen to higher volumes than normal. If our ears are missing presence, we simply raise the volume until we get the transparency our brains we need. That simultaneously raises the bass and treble giving it more excitement. I noticed that I listen to higher volumes with the Bird than I do with other IEMs. And, with some sources, when you turn the volume down, the Bird does not maintain an even response across the curve. That's my theory.