"Philippe Blain via GitGitGadget" [off-list ref] writes:

+The body of the cover letter is used to give additional context to reviewers.
+Be sure to explain anything your patches don't make clear on their own, but
+remember that since the cover letter is not recorded in the commit history,
+anything that might be useful to future readers of the repository's history
+should be in your commit messages, not in your cover letter.

I agree with only a half of the last sentence.

Things that are useful for "git log" readers should be in the commit
message (but that goes without saying---by definition "git log"
readers are reading commit messages).  If that material helps to
understand the overall topic structure by the reviewers, it is not
wrong to have that _also_ in your cover letter.  IOW, I sense that
"not in your cover letter" is a bit too strong.

Other than that, I found that 1/5 and 2/5 are very nicely written.

Thanks.