I always knew that in ArmA the optics are overpowered (as I also watched a lot through real optics) but I've been always too lazy to measure and analize this. This happened up to today when I've found a picture taken through a real ACOG so I measured the distances in pixels and compare the overall view to Arma's. I can understand that everything is related to the normal ArmA zoom to compensate the field of view and bring it closer to real eye accuracy, still there is enough room to improvement to make it more realistic.
So lets see. With a real 4x magnification, the height of the object appear, as it is normal, 4 times bigger than the original. What should be noted here is how accurate the object is seen through the optics. The building is like 350-400m away, you can figure out the size of standing man and realize there can be enough troubles aquiring the target even being proned.
At a similar distance (maybe even longer), in ArmA, the normal zoom is added to the 4x optics so the objects appears more than 8x higher. You can see that aquiring a target the size of a man is much easier, the optics behave more like a powerfull binocular than an ACOG. The effect is even more visible with 8x optics.
Conclusion: in order to balance the optics and make them more realistic, the optics should be downgraded to a lower magnification. If they are higher then normal zoom (like looking through an aimpoint), they are still realistic, aquiring a target at 4-500m with an ACOG shouldn't be just a piece of cake.