When I shot on the Range Active Duty in the Marines, we used A2's and had elevation adjustments, which also complicates the "understanding" of the zero somewhat.
Leaving elevation adjustments out of it, for simplicity.
If I understand it correctly, your sights/optics are setup to fire the round on an arc (its going to travel a ballistic arc no matter what you do) but its aimed upwards just slightly. SO, when you zero you sights, it will be dead on for 2 points on the arc. Where you zero your sight, will determine what 2 distances those dead on points will be, and how the other distances will vary in elevation at the other points. i.e. 50/200 meter will vary less in elevation than 25/350 meter OR 36/300 meter, except when you get out past 300 meters and then it drops off more rapidly.