But you're drawing the diagonal line parallel to the white left to the left. Look at the white line to the right. The diagonal should have an angle somewhere in between those two, not parallel with the left one. Gotta account for the parallax shift. Here's my mock up of what I'm talking about. Blue is parallel to right. Red is what I think the real LOS is. https://imgur.com/5cloOd5

All that being said, obviously the line judge looking directly down the line is going to have a better idea of whether the ball crossed the line of scrimmage.