My understanding of a –24db per octave L-R crossover is:

At an example crossover frequency of 80Hz, the low-pass section has started it’s roll-off below 80Hz. At 80Hz the signal is already –6db down. The high-pass section is complimentary to this. As the frequency rises, the slope upward crosses through 80Hz at –6db down and does not approach 0 db until higher than 80Hz. Since complimentary resistor-capacitor networks are used, and at the same rate of –24db per octave for both high-pass and low-pass, the phase shifts but remains coherent. With the same resistor-capacitor values chosen to halve the amplitude at 80Hz for both rising and falling frequencies, combining the two outputs for a test would show that at 80Hz, the two –6db levels sum to 0db, resulting in a close-to-flat response through the crossover point.

Maybe I need a better education on this?