The audio circuit can be deeper than the meter circuit. As Gary says, up to 15% deeper. Always trust the audio over the meter.
To my knowledge ,Up to a certain depth the meter shows you the Discrimination value digit readout ie, your numbers. Once you reach past the discrims limit ,your out of Discrimination territory & into All metal territory ,which the Discrim can`t go as deep as, hence you lose the Digital readout numbers , and get Audio signal sound only . Thats why sometimes you might get a "good" audio target signal without any Digital readout appearing, then you know the targets probably going to be at depth ,and then its up to your ears to decide.
I assume this is relevant to the Deus too.