See, ALL peterson pipe stummels are drilled to accept a filter, but not all the stems are. If that pipe is sold in Germany, the stem takes a 9mm filter.
The result, when bought as a non-filter pipe, as this on is, is that there's all kinds of empty space in the pipe, and the airflow is fairly turbulent because of it. I don't mind the concave end on the tenon, that's not a bad thing imho. But the pipe is not built to any kind of tight tolerance, that's for sure.
Keep smoking it, it may come around.