An angle of about 25 to 45 degrees above the face should be a good starting point, though you’ll adjust based on the shape of the face.
The higher you position the light, the lower the shadow will fall; place it too low, and you won’t get that nice butterfly shape, but move it too high, and the shadow will stretch down the face and onto the chin. An angle of about 25 to 45 degrees above the face should be a good starting point, though you’ll adjust based on the shape of the face.