The delay in the EP800v4 appears to be about 7 or 8 msec at 80 Hz. As Trevor said, the time delay, polarity and phase settings are critical. A difference of 5 msec results in 10 dB of attenuation at my MLP. Ditto with incorrect polarity and phase.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated