My head canon:

If the true value is medium high, any random measurements that lie even further above are easily explained, as that is a low ratio of divergence. If the true value is medium high, any random measurements that lie below by a lot are harder to explain, since their (relative, i.e.) ratio of divergence is high.

Therefore, the further you go right in the graph, the more a slightly lower guess is a good fit, even if many values then lie above it.