You forgot to \revert outside-staff-padding *before* applying
extra-offset.
Right, But even with \revert, the issue remains, because in any case the value of 0.56 for outside-staff-padding doesn't produce a shift. See:
%%%%%%%%%%%%%%%%%%%%%%
\version "2.19.45"
{
\override Staff.OttavaBracket.outside-staff-padding = #0
\ottava #1 f''' f''' f''' \ottava #0 f''
\override Staff.OttavaBracket.outside-staff-padding = #0.56
\ottava #1 f''' f''' f''' \ottava #0 f''
\revert Staff.OttavaBracket.outside-staff-padding
\override Staff.OttavaBracket.extra-offset = #'(0 . 0.1)
\ottava #1 f''' f''' f''' \ottava #0 f''
}
%%%%%%%%%%%%%%%%%%%%%
<text transform="translate(22.1264, 4.6976)" ...
<text transform="translate(35.1781, 4.6976)" ...
<text transform="translate(48.2297, 4.5976)"
I think there's no other way than the one I suggested:
1) extra-offset
2) \override some avoid-collision property with the help of a ruler set on the ref point
Best,
P