My old Excelsior has about 10 reeds where the leathers are bending back about 1/8" to 3/16". I've tried a couple of methods to flatten them but they are old and tired (kinda like me) and have lost their stiffness (kind like...well, never mind). I'd like to replace them but the information I've found on the internet says that if the leathers are replaced, the reeds will need to be retuned. Why is this so? The leather doesn't change the length of the metal reed in any way. So why would changing the leather reeds require retuning the instrument?