Gestalt said..
Needing to add 4cm does seem odd though. Are you using sails designed with lower clews and boom cutouts like the severne redback?.
I use Hot Sails KS3. On the smaller ones (3.1, 3.4), the boom cutout is lower than I'd prefer for the boom height I want, but just +2cm makes enough room. I have then been rigging most of my other sails at +2cm base just so I don't have to adjust the thing.
But I have ONE sail that needs +4cm...so I figured I'd just run them all at +4cm. Like I said, kinda silly...