The delay function allows you to keep the drivers in phase because the time arrivals are different for the ribbons versus the woofers. The Behringer was designed for pro audio applications where this is very important; otherwise, the sound won't be coherent at the listening position. As far as your issues with vocals it could affect that but without being there I can only speculate.

The amount of delay used will also vary depending on whether you measure with the ribbons on the inside or outside. A lower crossover point doesn't change things because the arrival time between the two drivers remains the same. One advantage of your active crossover is that it doesn't add any inductive or capacative phase shift like a passive crossover will.