You might use something like Speaker Workshop to set it up. Watch the overlap range between 1kHz and 3kHz, and adjust the LF and HF curves for best response. The mechanical slopes of the two subsystems are different, one being the roll-on slope of a horn and the other being the roll-off slope of a direct radiator, well into collapsing DI. That's why the electrical slopes you'll want will also be different.You'll find a second or third order LF low-pass combines well with a third or fourth-order HF high-pass, with crossover points slightly different, like LF at 1300 and HF at 1900. You could model the system, but it's a lot of work. Might be easier to just download Speaker Workshop and use it. At the frequencies of interest, it works pretty well.