Top Margin Adjustment

[Thomas Wilmot]

Hello,

In any LilyPond score, I always find the top margins to look abnormally small. 
I have tried to set top-margin, but for some reason, it is ignored.

Here is the file:

\version "2.14.2"
\header {
        title = "Why must my top margin be so small?"
}

melody =
\relative c' 
{ c d e f g a b c b a g f e d }

 \paper {
        top-margin = 5\cm
        annotate-spacing = ##t
        #(set-paper-size "letter")
}
 
\score { \melody }


Thanks,
   Thomas