You're right, of course, Dave. It is a 0.995 hit. The hit for sail area greater than 5% is 0.980.

For ease of reference, a N20 rates 59.3. Mark's rating, if he's not taking any mods on the jib, is 59.0. Unless his sail is really more that 5% bigger, which would rate him 58.1, almost the same as the M20.

Quick Sailwave run; Mark owes a stock 20 about 31 seconds an hour, while the "large" main owes the stock 20 just over two minutes an hour.