2.14.2 vertical spacing ungrouped staves...

[paul]

I am having some difficulty with what should 
perhaps be a simple task. I want to control the vertical spacing 
in collection of ungrouped staves. 
Reading some of the information 
online about such a task reveals its perhaps no so basic. 
Does one control this spacing in the \paper block in the 
\layout block or in the score. Also there are numerous variables 
one can change. 
Each time I attempt to control the vertical spacing, nothing
 happens.
The music I have typeset has too much spacing in between
 the staves.  
I am guessing this means 1) I am not changing the right variables, or 
changing them in the right way or 2) I am making changes in
 the wrong part of the 
source. 
I've tried changing system-system-spacing in the \paper block
 but I get no change 
in the output. 
I am using 2.14.2

Is there please some advice/examples on how to complete
 this simple task ?

Paul