If I'm crankin' flame on the ramp-up it might be less that 20%, I don't know. The whole thing seems a bit arbitrary; How do they tell the difference between smoke and steam?Try it sometime. 6 minutes and (essentially) no smoke from a cold start. That's year round. I can't/don't do the top down burns but even if you could I know it takes longer than 6 minutes to engage the cat and go smokeless.
Yeah, 20% doesn't look very dark, does it?Here is a chart showing what 20% opacity means. http://smokeschool.net/ringlemanchart1.htm