I second the minor surgery on the end of the reed. I play McCann reeds in a Dunbar poly chanter and that's the ONLY way I can make the F sound right.

A small block of wood also helps(lay the reed on it before chopping) I also use a new stanley type blade and a jeweler's hammer to gently smack the top of the blade.

It's a slow process as I never take more than a fingernail's with off at a time.

If this makes the reed too hard sand the soundbox as usual.