first bar width

[Federico Bruni]

I'm writing a blank sheet to be used for hand writing (see attached file).
The problem is that the first bar of each line is too large compared
with the other bars. I guess this is due to a default padding value of
some property.. I don't know which..

Any hint?

I've searched in the archives but I couldn't find anything, as I
probably miss the right keywords.

Thanks,
Federico
-- 
http://gnurag.net/blog/
http://fsfe.org/
http://groups.fsf.org/wiki/LibrePlanetItalia

\version "2.13"

\paper {
        indent= 0
        tagline= ##f
        top-system-spacing = #'((space . 10))
        between-system-spacing = #'((space . 13))
}

sheet= {
  
  \repeat unfold 7 { s1*4 \break }
}

\new StaffGroup <<
  \new Staff \with { \remove "Time_signature_engraver" } { \clef "G_8" \sheet }
  \new TabStaff { \clef "moderntab" \sheet }
>>