In the standard edition, Lesson 11 places the voice in this exact tessitura. It requires the singer to sustain notes right in the "break" area without pushing the chest voice too high or dropping the weight too suddenly.
The small grace note (usually a second above or below the main note) must be sung on the beat, taking half the value of the main note. Example: In 2/4 time, a quarter note with an appoggiatura becomes two eighths: the grace note sung as the first eighth, the main note as the second. vaccai mezzo soprano pdf 11