In the four π loudspeaker, the horn tweeter directivity is matched to the midwoofer in the crossover range. This allows a smooth transition not only on-axis but off-axis as well. Plus, the sensitivity of the woofer is just right for matching the tweeter's passive EQ scheme. You need about 10dB to provide conjugate compensation of the power response curve, and that's the amount of difference between woofer and tweeter, so it's a perfect match. There's synergy in that combination.