A/I ground gun lethality is controlled by 3 arena variables, one for each country. The specific variable is "GroundLethality" and has no effect on accuracy. It only effects the likelihood of damage when it hits you, not how often it hits you. I believe the MA is set to a value of 1.0 for all three countries. In the CT, we typically set it to 0.7. So, instead of the first hit castigating you plane, you might actually survive 2 or 3 hits with your parts pretty much intact.
Sabre
CT Staff, Reserve