I don't find the coticule is as dependable as Naniwa. I find it sometimes works really good, sometimes not. Thats why I love the Naniwas, you always get the same results over and over, and the edge is just really smooth. Btw the edge of a Coticule is good but I still like the Naniwa edge better.
If you want a bit smoother edge, I would add 30 laps on a balsa plate with Chromium oxide after your 12K Naniwa. You will definitely see the difference. You can buy it here for $15:
Sharpening Pastes and Sprays