Note: in Arma 3 zeroing settings aren't applied directly on scope inclination but they are converted into exit angle of the bullet from the barrel (you can easily check it using a bullet tracking script/mod ); I think there is an error in the code that manages these angles for every bullet and for every zeroing capable scope.
Note 2: Considering the real world physic, with some basic knowledges of trigonometry we can easily see that an ideal projectile will reach his maximum range when shooted at 45 degrees of inclination. In many cases, in Arma 3 when we surpass a certain zeroing value (that is different between every bullet-scope combination ), the exit angle of the projectile goes over the value of 45 degrees and we start to lose range instead of gain it.
English is not my native language, so I ask to be understanding if I've made some errors.
Regards, Michele.