My answer - it needs to match somewhat. I think you're right that if it matches exact you'll start out too flat. The other side is what happened when the main on my boat was purchased - the luff curve on this sail is more than the other mains I have, when it was first raised max downhaul was required just to get the wrinkles out. Obviously a case where more prebend was required to match the sail. Actually it was more of a case of the sail needed to be sent back, but you get the idea.