He’s said that most people, in any type of face-to-face conversation, automatically look to the other person’s face to read a response, and look at the other person’s body language, along with listening to words, tone, and inflection. This can be detrimental to confession, because the penitent gets involved in a person-to-person conversation with the priest rather than a person-to-Christ confession.
During face-to-face confession, we especially look at the priest’s face for his response–we can’t help doing so if we are human. We may be (unconciously) looking for affirmation, disgust, compassion, pity, understanding, shock, whatever. But we are looking for some human response. As a penitent, we should not be looking for human response, but for the forgiveness of Christ. Also, my priest friend doesn’t want to have to carefully control his facial expressions to project some expected response. He doesn’t want his facial expression to distract or dismay the penitenet. He wants to be able to focus on the sin, the counsel he needs to give the penitent, and not on affirming the penitent in a moment of extreme human vulnerability.
Another (lay) friend went to confession with this priest in a confessional room with a small screen. The layman asked for face-to-face and sat down across from Father. Father covered his own face with his hands, putting his elbows on his knees, bending over a bit, to avoid the facial expressions and eye contact.
None of my confessions with this priest have been anonymous. I have a distinctive voice and he knows exactly who I am–which he indicates by the counsel and suggestions he gives, and references to other conversations outside the confessional. Behind the screen does not equate to anonymous.