one should ditch along the direction of the waves (swell)
Waves and swells are not always the same, there can be waves on swells, which are moving a different direction.
For the Lake LA-4 flight manual:
"Swells: (avoid if possible) Movement: Always parallel, never perpendicular - regardless of wind. "
So, never land/ditch across swells, always along them. If only waves, land/ditch into the wind (which is probably into the waves also).