changing staff size in "\score" context

[Eby Mani]

Hi, I don't know how to change staff size in the following scenario, need to 
reduce the size of Organ staff in the score which should be given to the choir 
and vice versa for the Organist.

Are there any commands that can be used in "\score" context ?. I don't want to 
mess anything where the music part is.

I'm running Lilypond "2.16.0" on linux

Thanks & Regards,

Eby
*******************************************
global = { 
  \tempoMark 
  \tempo 8 = 132 
  \key g \major 
  \time 6/8 
  \set Score.skipBars = ##t 
\override Rest #'style = #'classical 
\compressFullBarRests 
\revert Rest #'direction 
  \revert MultiMeasureRest #'staff-position 
 
}

soprano = \relative c' { music }
alto = \relative c' { music }
tenor = \relative c { music }
bass = \relative c { music }

sopranoVerse = \lyricmode { lyrics }
altoVerse = \lyricmode { lyrics }
tenorVerse = \lyricmode { lyrics }

rightOne = \relative c' { music }
rightTwo = \relative c' { music }
leftOne = \relative c { music }
leftTwo = \relative c { music }

choirPart = \new ChoirStaff << 
   
  \new Staff = "sa" << 
    \new Voice = "soprano" { \voiceOne \soprano } 
    \new Voice = "alto" { \voiceTwo \alto } 
  >> 
  \new Lyrics \with { 
    alignAboveContext = "sa" 
  } \lyricsto "soprano" \sopranoVerse 
  \new Lyrics \lyricsto "alto" \altoVerse 
  \new Staff = "tb" << 
    \clef bass 
    \new Voice = "tenor" { \voiceOne \tenor } 
    \new Voice = "bass" { \voiceTwo \bass } 
  >> 
  \new Lyrics \with { 
    alignAboveContext = "tb" 
  } \lyricsto "tenor" \tenorVerse 
  \new Lyrics \lyricsto "bass" \bassVerse 
   
>> 
 
 
organPart = \new PianoStaff << 
  \new Staff = "right" << \rightOne \\ \rightTwo >> 
  \new Staff = "left" { \clef bass << \leftOne \\ \leftTwo  >> } 
>> 
 
\score { 
<< 
    \choirPart 
    \organPart 
>> 
  \layout { 
       \context { 
       \RemoveEmptyStaffContext 
       \override VerticalAxisGroup #'remove-first = ##t 
        
       \override DynamicLineSpanner #'staff-padding = #2.0 
        \override DynamicLineSpanner #'Y-extent = #'(-1.5 . 1.5) 
         \override TextScript #'Y-extent = #'(-1.5 . 1.5) 
       } 
         \context { 
           \Lyrics  
         \override LyricText #'font-size = #-1.5 
       } 
 
       } 
  }
**********************************************************************