I just saw Viking's new posts. He's probably in a tough position, a position of authority. Folks who ask him for rigging advice probably aren't willing to accept 'I don't know' or 'I'm not sure' as answers. So, he has to make generalizations. If he's off, folks will be stuck rigging that sail the way he told them forever, probably scarring them for life.
His general advice has some holes in it. That starting point of no looseness in the leech as a minimum setting isn't true for most modern sails. Also, his suggestion of 4 cm of range for the downhaul is a generalization. I took a quick look at 2 of my sails and the downhaul range on them was 5 cm and 2 cm. (The 2 cm was on an Ezzy!)
Eric, you'll be better prepared so that you don't have to ask someone on the beach.
Viking, being in your position, it might be good to suggest that, at the end of the day, they go home and check their rigging guide. That would probably be better for them in the long run. Again, you're in a tough position. When they check, they may find out that you gave them bad advice.