Here's the relevant info quoted from Nigel's site, it is equally true for Hamish and Finn's reeds too,
"If the chanter reed if playing at too high a pressure, and/or is flat and has a bold tone, then the lips need to be closer together, squeeze the bridle on the top and bottom of the reed. If the reed if playing at too low a pressure, and/or is sharp and has a weak tone, then the lips need to be opened, squeeze the bridle on both sides of the reed. A very small adjustment brings a big change in the way the reed performs, take care! It is very unlikely that you will need to cut the reed at the end, or sand it down. These other two principle adjustments have been done by us, the reed should be the right length and thickness when it comes to you."