Using WinIsd the ant trails smooth out into a really nice clean interstate across Nebraska leading me to believe I could crossover anywhere between Norman and Salt Lake City.

The plot has that mountain range between 900 and 1500 hz just as you say. If the box doesn't smooth that out, does that mean it must be crossed no higher than 900 Hz or will the choice of type of crossover do that?

I woul;dn't like to use the tweeter much below 2000 Hz if possible, less for safety than to get the crossover point well above the primary treble range of voices and instruments.