This shows exactly what I was saying. In the top diagram it is sighted in for 50 yards. Anything inside 50 yards will hit low. The closer to 50 yards you get the less sight offset there is.

When we do our quarterly rifle qualification there is always someone who forgets their offset on a headshot when we do them at 10 and 15 yards and drops a round under the scoring area if the head. You have to aim a couple of inches high. We zero for 50 yards.