Middle of the face, and probably more like 51.8° originally. That corresponds to base faces measured in turns of a measuring wheel and a height of the same numb

Middle of the face, and probably more like 51.8° originally. That corresponds to base faces measured in turns of a measuring wheel and a height of the same number of wheel diameters, which would be an incredibly sensible way of laying it out (letting the tools do the calculation for you).