The midhorn used in the six, seven and eight π speakers is a hifi midhorn and doesn't go low enough to be used as a top box for the 12π basshorn subwoofer. That's what the 9π is designed for.

Assuming you mean the midhorn used in the six, seven and eight π loudspeakers, below is a measurement of it using an Eminence Delta 10. This horn is designed to be used between 250Hz and 1.6kHz, and the crossover designed for it takes into account physical placement of the midhorn, woofer and tweeter so that summing is good.

π midhorn with Delta 10 driver