DH-3N20 bearing adjustment

What's the conventional wisdom for setting preload on
Shimano hub dynamo bearings?

On a normal hub I'd adjust the cone finger tight and
set the locknut without moving the cone. The dh-3n20
hub is quite a bit more limber owing to the diaphragm
like ends.

If more preload is needed, how much?

Thanks for reading,

bob prohaska