JJ, I don't have my old 852 course here, but it sure seems like that engine load is a correction factor for ignition. The Autoshop page(older course) on TCCS says the same thing. edit; It says engine load is a base factor, along with Ne and G1. Not a correction.
Jimmy, I didn't mess with my timing when I lived in Denver. We have a closed loop timing circuit. Not very advanced mind you, but the gains were not noticable, if they existed. Measured by the butt meter. Unlike an EEC-IV Mustang, which is set(advance), and changes to base are noticable. As total is effected.