Summarizing the previous posts:

- Rudder's turning forces (LIFT) occur and are measured for optimization at HIGH angles of attack.
- Board's lateral forces (also LIFT) occur and are measured for optimization at LOW angles of attack.
- Hull's DRAG forces occur at LOW angles of attack and are usually measured for optimization at NO angle of attack.

Optimizing a foil's surface at HIGH or LOW angles of attack are two different things.

Optimizing for minimum absolute DRAG is not the same as optimizing for MAXIMUM LIFT or for BEST LIFT/DRAG RATIO.

Conclusion: the optimal surface for each of the three situations must not necessarily be the same.