When goal umpires make mistakes, people often say "I don't understand, the goal umpire was in perfect position!"
But think about it, if you're trying to track a moving object (like a ball), the closer it gets to you, the faster it appears to move. For example, imagine standing on the side of a road, and watching a car drive past. As it's coming towards you, you can easily track it's movement. But when it passes right by you, it's moving "fastest" according to your perception.
So really, I think the position goal umpries are standing in (directly under the goal) is pretty much the worst possible place to spot deviation in movement, like what happens when a ball grazes the behind post.
But think about it, if you're trying to track a moving object (like a ball), the closer it gets to you, the faster it appears to move. For example, imagine standing on the side of a road, and watching a car drive past. As it's coming towards you, you can easily track it's movement. But when it passes right by you, it's moving "fastest" according to your perception.
So really, I think the position goal umpries are standing in (directly under the goal) is pretty much the worst possible place to spot deviation in movement, like what happens when a ball grazes the behind post.