Originally Posted by flo617
Sorry, I meant that the sock forces to use a slightly shorter sail since it messes up the sail shape if there is not enough clearance on top
That is correct, you need a bit of space for the sock to bunch up. I believe some socks even have a strop or rod built in to them for this purpose.
Make sure you have planned out where you are going to fly the sail from before you size the sail. If you think you might want to use a sprit, make that decision before you order the sail. Once it is built there is no going back!