I am a math doctoral student. Recently, I received a revision of one of my articles.
It is a positive report. In the report letter, the referee advised looking into a particular project (a significant project, not an indivisual project) and connecting it to my paper to give the impression that my work has a wider readership. The report might advise citing some of the project's work. Though there were a few links, they weren't really strong, so I found less of a connection between the project (referee mentioned) and my paper. I've talked about this with a few people working on that project (referee mentioned), and they've said they'll try to expand their project later, which might strongly tie their project to my outcome. However, it is uncertain, and I cannot hold out for them for so long. In the interim, I discovered similar projects where my work is directly applicable. To put it another way, my results are more relevant to a different project.
Now that I have revised the paper, I would like to send it back to the editor.
How do I inform the editor that we have discovered a slight connection with the project the referee mentioned, but have instead found a similar project in which my results are more significant than the project (referee mentioned) and have revised the paper accordingly?
Should I write a distinct cover letter to the referee via the editor? Or should I simply disclose every detail to the editor and send only the revised paper?