With both eyes open the mind will impose the reticle onto the target in such a way that it is clear, and the reticle is always in focus on the target. I can place it onto targets across a room with no real effort. Anyone that practices with it much would love the way the ACOG works.
As a side note I need glasses to see 20/20 far off, but I'm not that bad. I noticed I can leave my glasses off and what ever I look at through the ACOG is crystal clear to the point that it is actually easier for me to shoot at distance with my glasses off.