(The group in your picture is probably due to firing different ammo than normal, but read the rest of this.)
Point of aim and point of impact only cross at two distances, occasionally only one.
For rifles not set up for competition fixed-range shooting, it's better to zero them such that the variation from point of aim is minimized for the furthest distance.
For instance, maybe your options are:
1. Zeroed at 25 yards and 300 yards, but 6 inches high at 100 yards
2. Zeroed at 33 yards and 200 yards, but 3 inches high at 100 yards and 8 inches low at 300 yards
3. Zeroed at 100 yards, but 2 inches low at 33 yards and 18 inches (!) low at 300 yards
Pick one, then take your rifle to the 100-yard range and bang away without adjusting your elevation. Only in the worst case (3) will your groups be centered.
For small variations like in your pic, different ammo or different positioning of the rifle on a rest can also make the difference.
What makes the jobs of military and police snipers so difficult is that they have to be able to land a single round precisely on target at unknown distances and without a test round. That means they must be well versed in the ballistic behavior of their rifle and ammo, and must be extremely good at judging distance.
(ETA: Actually, the pic in the OP looks exactly like what a 100-yard zero from a scope or high irons will do at 50 yards without adjustment.)