You'll get the best out of your naniwa if you do some figure 8 laps on the naniwa before each use. That will also helpp you avoid major lapping sessions periodically.
+1 to this. I've been using Glen's system, in which you do 5 figure 8's (I use a DMT 325) on the Nani ss before you use them. I've been getting very good results. Plus, it keeps your stones clean and lapped.