In the case of the mid-bass horn, the throat transition does not affect the sound enough to worry about IMO. Due to the narrow bandwidth (100Hz - 1000Hz) the step transition between the woofer cone and horn throat is acoustically invisible. In order to have cancellation you need a reflection that is half a wavelength away from the source (i.e. the cone). The longest distance from the cone to horn throat is about 2-1/2 inches. This corresponds to half a wavelength at 2700Hz. So, our upper range of 1000Hz is in no danger of being screwed up by the throat of the horn. The 1000Hz wave is too long to "see" the throat transition. About the only thing one might wonder about is whether the upper harmonics that help to develop our tone are being affected?