Before recording the calibration video... There is a button for "evalutaion". This must be clicked on before I can start recording.

I've noticed that if I "darken" the scene for calibration, then record, then playback... I can see sort of a shadow copy of the background. If I go darker it's worse.
Does someone need to be standing in the scene for this or does the scene need to be void of anybody standing there?

If I don't darken the scene, I don't see the shadow of the background, but then the problem is that it doesn't square no longer stays on the point of light, but bounces around to other objects.

When the software evaluates a background, the scene should be empty. The reason for background evaluation is to easily clear an action (or calibration) video from unsignificant details (i.e. - "background").
If you change the setting for "darkening for calibration" after the background has been evaluated, then you must re-evaluate the background, because it does not match to what cameras see anymore.

Thanks for the advise.

Just to confirm... I have to darken the scene for calibration... Evaluate... Then film the calibration with my mag light.

Once done.

I will set the darkening back to normal. Re-evaluate the scene... Once done... Then I can film my actor performing.

I assume that darkening for calibration and then filming the scene lighter for action, is not going to be a problem?

Yes, you've got me right.
It is necessary to reevaluate the background each time the picture in cameras changes considerably. After changing camera settings (like "darkeining for calibration", "exposure" etc), after lighting of the scene has changed and so on.
Of course, you can shoot different videos with different settings. Just make sure to have an adequate background evaluated before each shooting.