MarcM just reviewing the logs, it looks like you cleared the cache for the whole domain on 4th December - this will cause the cache rate to drop further until the pages are revisited by users and recached, so for some pages this will take a while if they don't receive a lot of traffic, so it's best to just clear cache by URL when you update a post on your website as this allows the rest of the site to remain cached, and then you can allow cache hits to build up over the next few weeks.