Spaced score

[Sebastiano Vigna]

It is my understanding that overriding shortest-duration-space like this

        \context PianoStaff <<
           \time 3/8
           #(set-accidental-style 'piano)
           \override PianoStaff.SpacingSpanner #'shortest-duration-space = #10.0
           \context Staff = upper { ...
           
should give me a more spaced score, but absolutely nothing happen. Where's the 
mistake?

-- 
Ciao,

                                        seba