Staff spacing

[Richard Opheim]

In the example below,
 
\version "2.14.0" 
\layout {\context {\Score   
}}
<<\new Staff = "main"
\with {\override VerticalAxisGroup #'staff-staff-spacing = #'(basic-distance . 
3)
}
{\time 6/8 
%{1 %} r8 g8 [ b8 ~ ] b8 [ d8 f8 ~ ] 
%{2 %}<<{ f8 [ f8 f8 ~ ] f8 d8 r8 %{3 %} r8 g8 [ g8 ~ ] g8 [ e8 c8 ] ~ } 
\new RhythmicStaff \with {alignAboveContext = #"main" fontSize = #-3
\override Stem #'length = #5
\override Stem #'length = #5
\remove "Time_signature_engraver"
\remove "Staff_symbol_engraver" 
\remove "Bar_engraver"
} 
{ b4 b8 r4 b8 r8 b4 b4 b8}>>
%{4 %} c8 a4 r4 f8   
}>>

 the staves are too far apart. 

It was my understanding that changing the value in parentheses in
 
\override VerticalAxisGroup #'staff-staff-spacing = #'(basic-distance . 3)

would alter the distance between staves, but though I attempted to do so, the 
staves remained at the default spacing.