Actually, I simulated my horn (as is) in HornResp about a month ago. I modeled the Delta 10A, since you already showed that it worked well in a front-loaded horn, plus it was an inexpensive choice at Parts Express. The throat, being a slot, wouldn't model just using the total area, so I pretended that it was a square of the smallest dimension (the width). The horn was modeled in 4Pi space as the worst-case scenario for a live SR subsystem. One box was a little disappointing, but 4 boxes stacked as a line array --usually the minimum box requirement for most pro audio line arrays-- flattened right out and rolled off close to the lower cutoff target. The upper cutoff was a little higher than in your Midhorn (which I used as a reference point, thank-you) though it was inconclusive whether the 2kHz goal was met.