Kretschmer, Lüth and Topp have some 13-17k tons average out of the 14-16 patrols. Merten, Schütze and Schltze have 21-36k tons, but less patrols (5-8).
They are the most sucessfull commanders, and we should compare only with them.
The most successful patrol was that of Hessler in mid 1941, when he sank 86000t.
My average patrol is around 70000t, so that is far from realistic. I do use manual targeting, but not 100% - I have map updates on and external camera (for screenshots

), and some other stuff, which IMO doesn't realy have any effect on realism.
What is your average torpedo hit percentage? I would estimate mine to about 75-90%.