This is all correct.
Don't worry about level or elevation. As long as your hand is not applying radial forces to the butt of the cue at the moment of impact, you should get a high score.
After 798 shots on the advanced level nearly all my straightness shots red-lined. My average was 6.87. From reading the above, maybe I need to deliver the que in a "throwing motion" in order to eliminate any radial force from my right stroking hand. I can usually green-line most of the other parameters but straightness escapes me for now. I want to follow this thread to try to figure out the flaw causing straightness red lining. Hope we can get more input here.