In Bottoms UP! I suggested that the choir is better served by having the piano cue them from the bass up, not the top down. Here’s another piano Cue Tip that is helpful to the ears.
Reinforcing part singing in rehearsal is a key function for the pianist. And sometimes when things aren’t being picked up quickly the player is compelled to play louder . . . banging away at the part until the offending line is mastered, or until a fingernail is broken . . . whichever comes first!
As a rehearsal pianist myself, I’ve seen the value of playing the part that’s being isolated in octaves. This works because it gives the singer a second reference point. After all, the singer is attempting to sing the note ‘at pitch’, and the ear is sometimes challenged to hear that note being simultaneously sounded by the piano. To overcome this, for the men, I play their part plus the octave above. For women, I play their part plus the octave below. Playing the men’s part an octave above keeps the reference out of the muddy lower range. Playing the women’s part an octave below keeps the reference within the normal sung range of the choir. (Although sometimes it might just seem better to reinforce the women at the octave above, but not as a rule.)
So here’s another Cue Tip for the rehearsal pianist: The best way to reinforce a line in rehearsal is to play it in octaves, so that there is an external pitch being sounded which the ear can use to anchor the notes. Think of it as triangulation . . . i.e. the same way a GPS system works . . . by having two points of reference yielding an exact location on the ground below!