More downhaul and outhaul both will flatten a sail and de-power it. However, downhauling will also loosen the leach and add more twist which outhauling won't.
Rigging to specifications if on the correct mast doesn't always mean that the sail is rigged correctly. New sails need to streatch a bit before you can reach the correct downhaul without over doing it. Older sails may need a bit more dowhaul to get them right.
Mast extensions are all a little different than their marking in centimeters indicate.
Variations from the recommended downhaul and outhaul are normal for additional power or decreased power based on conditions.
Bottom line is that it takes experience to see and feel if the sail is rigged correctly. There is no one correct answer. Many people may think they have it correct when it's not.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.