keeping fx return out of mono mix even when fader not raised

hooty77

Using 2 mono mixes to 2 headphones. Problem hearing fx return from another channel even when that channel is not sent to mono mix. If that channel is then raised, the input signal is properly heard and mixed with the fx. This is a problem if an artist does not want e.g. another mic input in his mix but does want ‘their’own fx’d signal in their monitor/headphone mix, & he/she hears the fx return from the other mic as a ghost in their own mix. what am i missing here? thanks in advance for any ideas. p.s. do i need to use 2 separate fx on main input layer for each channel?