I always had trouble with incident-meter readings until I realized one simple fact. When pointing the meter at the camera, the camera has to be in the same light as the subject. IOW, if the camera is in different light, point the meter at a location in the same light as the subject as close as possible to the camera position.
The light on the camera is irrelevant. With an incident meter, you should read the light falling on the subject. After all, that's what you are taking a picture of... not the camera!