How to limit the NoteColumn shifting

[Pierre Perol-Schneider]

Hi List,
The NoteColumn default shifting is about #.5 ; I'd like to reduce it
globally, let say by 2.
How should I do?

%% SNIP %%
\version "2.19"
\fixed c' {
  <<
    { g'4*2 8 } \\ { g,4*2 8 } \\
      %% Wanted:
    { %\override NoteColumn.force-hshift = #.25
      b4*2 8 } \\
    { % Wanted:
      %\override NoteColumn.force-hshift = #.5
      \stemUp\shiftOnn
      d4*2 8 }
  >>
}
%%

TIA, Cheers,
Pierre