I am actually a little curious how you're getting the numbers you're getting.
Aaron Rodgers, for instance, has a career AV of 150 and 142 games played per PFR. So 150/142*16=16.9. I also wonder if it'd effect anything if you used games started vs. games played and only used AVs from seasons with starts. For Rodgers that'd change the numbers to 149 AV, 135 Starts, and a score of 17.7. Score went up because his 0, 0, and 1 AV from his first 3 years with no starts are factored out.