Stereophile's measurement of the Eggleston looks like a classic case of a tweeter that is wired out of phase from the correct orientation. The very deep and symmetrical suck out is the result you get when a crossover designed to match the tweeter and mid phase at the crossover point is wired out of phase.
I'm guessing, but from the layout of the baffle and the shape of the dip at the crossover point, this was meant to be a Linkwitz-Reilly 4th order crossover between mid and tweeter, and a tech simply connect the tweeter backward.
I'm guessing, but from the layout of the baffle and the shape of the dip at the crossover point, this was meant to be a Linkwitz-Reilly 4th order crossover between mid and tweeter, and a tech simply connect the tweeter backward.