From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer rules that the entire glans must be exposed down to the groove for a valid circumcision, rejecting the claim that one-third suffices; the Terumas HaDeshen's one-third measure applies only to correcting a circumcision that grew back, not to the original act. He concludes that mohalim who refuse to comply with the communal rabbi's rulings should be removed from their positions.
Source: Shu"t Chasam Sofer YD §248