Incident metering measures the incident light in the shaded areas, not the intended black point on a film or paper curve.

Assume for a second that you are doing a backlit portrait, sun behind your subject. The "highlight reading" is taken from the sunny side, meter on the back of your subject's head, the "shadow reading" is under your subject's nose. The "shadow reading" by itself places the face at a fairly normal zone 6ish in relation to that reading.