I remember it used to be a button under the article. I don't know when it was moved to a sub-menu under the author's name.
Personally, I think it's a bit unintuitive to put it there. I wanted to report an issue with articles; I have no issue with the authors (I'm sure they're all nice people, even if they make the occasional mistake! )
If an issue is caught/reported quick enough, we'd see more relevant comments, and less of them of just people pointing out the obvious (guilty of doing so myself just today, since I couldn't find the report link...)