Continued.
This drawing illustrates this point.
Basically what's happening is the bullet is crossing the baseline at an upward angle at 50 yards, and crossing the baseline/line of sight at 200 yards on a downward angle.
This setup, sometimes called a 50/200 zero, allows for a fair degree of precision at both closer range and longer range.
At very close range, 20-25 feet, your bullet will strike 1 1/2-2 inches below your line of sight, depending on if your using irons or optics, and if the optic is true or 1/3 cowitness. Regardless knowing if your bullet is above or below line of sight, and at what distance, is important to hitting your target, or NOT, depending on the size of your target.
A 50/200 zero will have your bullet above/below line of sight no more the 2 1/2 inches out to 250 yards, give or take. So if your target is bigger then 5 inches in diameter and you zero 50/200 then you can aim center and hit it out to 250 yards, making 250 yards your maximum point blank range, or the distance you can hit a target without making a sight adjustment. This is all based on standard AR ammo and barrel length. Going to extremely light/fast or extremely heavy/slow bullets, or extremely short barrels will affect your zero and point blank range.