Right now you can zero your weapon in 100m steps from 100 to 800 depending on how the weapon has the feature. But thats not how you would do it in the real life. In RL you have to rotate a wheel on for example the sniper scope to higher or lower its inclination to the weapon in degrees.
A system like in the ACE mod of ARMA 2 would be enough. Just replace the 100 with degrees. For example 500m would be than 9°.
Just imagine that you would find a Mosin with a long range scope. As a normal person you wont have any clue to use it properly. For example you would find this wheel on the scope and you wouldnt know which distance to which degree belongs. You have to test it. In vanilla you know it right away.