I did that. It's well below the 20% mark. But it's either not clearing the cache at all, or some things come thru that won't clear. It seems to take about a week, typically, for things to go pear shapped.
The issue isn't that it's not working at all, it's that the cache fills up and doesn't self clear as it should. And I don't see any reason for it.
I followed a reasonably good guide to set up, and it included some settings for cache size in 'if your hd is X, don't use more than Y' type info. And I've decreased it since then (now below 3gb on a 5gb drive). So I don't know what's up.
But thanks for being a smart ass and not really reading what's going on in my first post. B/c the lmgtfy link was for general set up.