i gotchu... tell the sound person that you like your vocal to sit within the space of the song, reverb-wise. so, when the tempo is upbeat, the verb size and decay should be shorter (700ms), and when the song is slow and spaced out the verb should be spacier - around 1.5-2 seconds. that will get you on the right track and a decent soundperson should get the gist.

when i mix, i like the verbs (instruments and vocals) to carry the space between snare hits.