I have connected the effecter to the SEND/RETURN terminals, but the Echo effect tail cannot be heard after the fader is closed. Why is this?

When INSERT is selected from the RETURN TYPE of SEND/RETURN and the effect channel is set to the respective channel, you cannot hear the Echo effect tail. Post-fader effects allow the Echo effect tail to be heard even after the fader is closed when CROSSFADER A, CROSSFADER B or MASTER is selected as the effect channel.