First, take a look at the fin you have.
Run your fingers over the graphics and stickers on the foiled surfaces.
If there are any bumps/lumps/valleys that disturb the smooth flow of water
over the foil, you need to wet sand your fin (use 400 grit wet/dry abrasive paper or
one of the sponge sanding blocks in fine grit) and smooth out the foil.
Another fin , perhaps a bit larger than 30 cm may help alot also,
If you still have your old boards (or can get near them to measure, compare where the
mast foot and the footstraps/fin are located on the board. If there are large differences
in mast foot to fin, and fin to rear footstrap measurements, then yes, you will need to
sail the Kode differently.