Johnk, you probably already know this, but my suggestion would be: Don't equalize the on-axis dip you get in the treble region. It's an artifact of the in-phase mouth reflection; it moves up or down in frequency as you move the microphone closer or farther away, and it disappears once you're off-axis by 15 degrees or so. Just listen from off axis anyway and the mouth reflection dip becomes totally inconsequential.
Ralph, in my experience, conicals and quasi-conicals beam less than exponential or tractrix horns, and in trade-off require a more complex crossover. Several of my models use what conical guru Bill Woods has described as a "conical horn", including the Stormbringers that made a stop at your place a while back.