[throwaway25239]

Thanks for the suggestions. I think those 4 all look OK. The site content is purely static HTML (and some images) that hasn't changed significantly in months, so I'm guessing that's not the issue.

I'd rather not post the site URL here; is it OK if I email you?

[franze]

Honestly, as with most other tools that you have to care about but don't want to: just follow the spec https://support.google.com/webmasters/answer/6033049?hl=en