Red dot moving the bullet?
Ok. Look at this chart that describes the flight of your bullet at different zeroing distances:
Note: The dotted horizontal blue line marked 0.0 represents your line of sight. The colored arcs represent the path the bullet takes.
The red dot doesn’t move the bullet.
The dot represent where your line of sight and the path of your bullet intersect in space at a given distance from the muzzle.
See, the instant you press the trigger, gravity starts working to make your bullet fall to the ground.
Hold a bullet in your hand and extend your arm parallel to the ground. Now drop the bullet. The amount of time it takes the bullet to hit the ground is the same as if you fired it from a rifle (if the muzzle was perfectly parallel to the ground).
To counter this, so we can shoot further, we adjust the sights to angle the barrel so it isn’t parallel to the ground. This angle gives the bullet a ballistic trajectory.
Your eyes to not see on a ballistic trajectory, they see in a straight line.
Therefore your line of sight (which is a straight line) and the path of your bullet (which is an arc) are not the same.
The bullet, will intersect the line of sight 2 times - once while rising (because the sights are above the muzzle) and once while falling.
With a 25 yard zero, the bullet is still rising the first time it crosses your line of sight and will continue to rise until about 225 yards - where it will be almost 8.5” above your line of sight (that means if you want to hit something 225 yards away, you have to aim 8.5” low). After reaching its maximum ordinate at 225 yards, the bullet will start to fall and cross your line of sight again at about 375 yards.
All this should tell you is that a 25 yard zero sucks for anything other than shooting 25 yards.
I have found that the 50yard zero is the most useful for a shooting an AR.
Zero at 50 yards and your bullet will intersect with your line of sight at 50 yards (while rising), maximum ordinate will be reached at about 130 yards and only be about 2” high, then start to fall crossing your line of sight again at 200 yards. Much more useful. You put the dot on the target and you will hit within +/- 2” from 25 to 225 yards.
Mechanical offset will still rear its ugly head inside 25 yards and you will have to adjust accordingly - but that is regardless of zero.
*This is all considering you are using a red dot optic on an AR type platform.