well, "a few" FG writes is not bothersome, what's important is how this number relates to your LRU and Chunk writes. I suspect that with only one cleaner (Gag!) and your ratios set that high that you have a very high rate of chunk writes - which is what you really want to reduce. You have 60K dirty pages before you start to clean!
As a starting point, for cleaners, two per device. Drop your LRU max and min to as low as 5/2 or 2/1.