I'm only guessing, the smallest dimension looks closer to 3". Measurements would be more revealing.
Pretty much all drivers have a high frequency power response rolloff due to mass and inductance-like effects. When you put on a horn or waveguide...hmmm not sure how to describe what I'm thinking. Something like that if you really load a diaphragm to generate pressure, if you spread that pressure evenly i.e. constant dispersion, then the on-axis response will be falling off. If the on-axis response is flat, then just like a loose tweeter, the off-axis response will be dying. Personally I'm wanting to have a really consistent response out to the coverage angle, figuring I can EQ the whole thing flat.