When a person is tagged in a comment in a proof they receive a notification, but when they click through, they have to figure out how to find the comment by some magical combination of looking for the comment number or searching for a word or person and then scrolling to figure out where it is in order to reply.
When there are 500 comments in a document, it is time consuming and frustrating.
The comment notification should link directly back to the page in the Proof where the comment was made.