I think the 1.6KHz crossover is the best choice. Off-axis response above that probably drops like a rock especially once the drivers in breakup modes, good idea having the compression driver take over instead.

Have you taken the 2nd, 3rd and 4th graphs indoors or something? They all seem to have a lot more response below 300Hz than the 1st one does.

Is the rear facing midrange you talk about just the woofer in the cornerhorn's?

Did you run into problems with the edge of the cone in the midrange horn slamming into the mounting plate? This was a problem I found in my horn at high levels. It was clear as daylight to hear it when excursion was high at high SPLs, awful sound it makes. I had to add a ring between driver and mounting plate, and add another piece between cone and front chamber to bring the volume back down again that the ring displaced in the front chamber. Or you could just route a circle groove in the mounting plate where the edge of the cone meets instead.

Good job!