Dotted ottava bracket

[Noeck]

Hi,

I would like to change the ottava bracket style. The markup line on top shows
what I want, the dashed ottava bracket is the closest I could achieve. However,
I want it to look like the dotted line on top.

\version "2.18.2"
{
  \override Score.OttavaBracket #'style = #'dotted-line %why is it still dashed?
  \override Score.OttavaBracket #'dash-period = 0.6
  \override Score.OttavaBracket #'thickness = 2
  %\override Score.OttavaBracket #'dash-fraction = 0.01 % does not really help
  \ottava 1
  a''4^\markup {
    \override #'(thickness . 2)
    \override #'(off . 0.01)
    \draw-dotted-line #'(10 . 0)
  }
  a'' a'' a''
  \ottava 0
}

Can anyone help me out?

Joram