I didn't measure the midhorn with the 2123, so I can't say for sure. The 2012 rolls off pretty early, and response is clean. It sums nicely with the crossover as shown in the plans. I would guess the 2123 would act like the 2012, but it might be more like the Delta 10, which has more output above 2kHz. This is determined largely by the dustcap.The thing to watch is HF behavior, and the crossover between midhorn and tweeter will be determined by it. Most start to rolloff between 1kHz and 2kHz and the trick is to match this with the tweeter so that summing on and off axis is good.