If your trying to fatten up the vocals, then keep the efx minimal. You shouldn't notice the efx, until you turn them off. I sometimes use a stereo delay/pitchshift, that will fatten up a singer with a thin voice. I run the send to efx unit, set one side for a +1 pitch increase and the other for -1 decrease. Then delay each side a differant amount, all are set to 100% wet. I bring this back in to a stereo channel, turn it up until it is noticable, then bring it down until it is just thickening the part, but not a noticable effect.