I'll Decide ...
Level 5 Referee
All seems fairly pointless to be honest. ?Until recently (last couple of seasons), the instructions were to stand in line with the edge of the goal area and ensure the ball was placed on the line or inside the goal area. It was felt that ensuring the assistant was back up in line with the 2nd rear most defender was more important than ensuring the ball was placed correctly. The instructions were changed so that the first kick in each half was checked to ensure the ball was correctly placed in the goal area, from a position in line with the edge of the goal area, for the first goal kick of each half. After that, each kick should be checked from a position in line with the edge of the penalty area (i.e. 16.5 m from the goal line) which gave the assistant a 16.5m head start on the run up to the 2nd rear most defender.
Hope that make it a little clearer.
You don't actually NEED to be exactly in line with the goal area to see that the ball has been correctly placed (ie not outside it).
And in any event, by the time GK has placed it, walked backwards, paused, and taken his run-up, unless you're grossly unfit, you've plenty of time to get back in line with the 2nd rear most defender.