Point the incident dome toward the camera lens from the point of view of the subject, just like a light meter. Do this regardless of what kind of lighting situation you are in. You are measuring the color of the light falling on the subject as seen by the camera.
Multiply the filter factors.
A two color meter will not compensate for green, only red and blue. It would be better, in my opinion, to use your mired filters and add a CC20M filter for the green to get very close to correct.