@mihorn
While the diagram you provide is true, I don’t know of any theory of speaker dispersion that matches your description.
I suggest you take a look at ANY midrange or woofer spec sheet and examine the of-center frequency response, as well as any of the lateral dispersion charts from Stereophile.
In all these cases the overwhelming issue is the diameter of the cone relative to the wavelength, and the shape of the driver, be it cone, dome, or even flat doesn’t play a big role.