No, the correct(intended so far) value is -50.So are you saying we should change the 50 value to a -1. Is that the "correct value" instead of -50?
If you want to make it that ranged cities hit extremely hard, it's -1 or 1 (never 0 since 0 times something leads to fun results). Ranged Attacks of Cities haven't matched the actual City Strength since vanilla (even ranged units don't have the same ranged combat strength to combat strength).