Great answer Drew eckhardt,
As a devotee for years of First Order Crossovers because of the phase correct delivery, I overlooked the directionality that they impart.
Its almost as if the Laws of Physics conspire to give us that dogmatic, equal and opposite thing in every category.
Comb filter effects, off axis aberrations in frequency response...as mentioned narrow 'sweet spot'...all negatives.
So when I designed the LSA Loudspeakers, one goal was to use a crossover that did NOT limit listening position as much.
My (now ex) wife used to say, 'I can only hear 'this' speaker, pointing to the one in front of her.
In experimenting, by using 2nd, 3rd order in my design, as well as the now more popular radius side wall cabinets, almost all of the directivity is gone.
I must admit to almost arbitrarily sitting closer to one speaker nowadays...just because I can and it's somehow liberating...certainly not confining.
Again, good answer and interesting thread.
Larry