I'm not sure there. I do know that if you have a unti of 5.6 hitting both sides of the face, and one unit of (2x5.6=8) hitting one side then that is 3:1, with 3 units on one side and only 1 on the other. However when you meter that with a meter (incident) pointed at the camera from subject you get 8.3 to 8.5 total exposure. Maybe that is where the extra 1/2 stop is coming from.

Now what to answer on the test....