As the rule was quoted in that article, the ball is placed at the foremost spot of the ball as the ball crosses the sideline.
In reality, you'd need an absolute overhead shot to know for certain where the ball is when it crosses the plane of the sideline, so you have to use your judgement to spot the ball. That's why they pay us the big bucks.
I mean, it's not a lot of bucks, but the font is very large.
It would most certainly cost a lot more bucks to install a multi-camera system to track the ball in space, like Hawk-Eye, but I don't know if that works well for the ball held in a player's hand and not in a free trajectory.