textspanner too short

[Tiago Morin]

Hi lilyponders

I'm having some trouble with the textspanner line. In the following example:

\version "2.10.33"
\paper {
  raggedright = ##f
}
\score{

\new Staff{

<<{e''8.[ c''16] b'8.[ c''16]
\once \override TextSpanner #'edge-text = #'("III" . "")
\once \override TextSpanner #'direction = #1
\once \override TextSpanner #'style = #'line
\once \override TextSpanner #'edge-height = #'(0 . 0.5)
\once \override TextSpanner #'dash-fraction = #'()
d''8.[\startTextSpan e''16]\stopTextSpan }\\{g2 <e c' g' b'>4 }>>
s4 s s s s s s s s s s
}}

the spanner line is not printed, still I think there is some space
left to print it. It seems to me that the text is printed far to right
related to the note head it refers.

Is there a way to offset left the text so more space is left; or
center the text to the notehead; or reduce the gap between the text
and the line?

Thank you

Tiago