I am not an expert on blaistics and I might be totally wrong here so if I am dont yell at me too much. MY common sense look at this would be as follows.
If you picture a laser straight line coming out of your scope and the barrel is an inch or two below. When the projectile leaves your gun it will initially be below the line of your cross hairs. The bullet will at one point cross this line and travel above it for a distance and at some point will cross the line again as it begins to drop off. Now depending on what type of round and the speed of that round would obviously play a huge roll in all of this. So in my mind there will be two points (one close and one further away) in which the bullet will be dead on.
Does this make sense to any one else or am I an idiot.