difficulty filling the whole page

[Jean-Alexis Montignies]

Hi there,

I've written a score and after playing with spacing, and margins I made it a 
one page score.
But at the end of the page, there is about 20 mm left. If I increase the top 
margin to 1mm (it's 0 for now as is bottom margin), lilypond add a second page, 
though obviously from the human perspective there is still plenty of room :)

Any clue?

Greetings,

Jean-Alexis