collision between slurs and and tuplet

[Stefan Thomas]

Dear community,
in the first of the  below quoted snippets I get a collision between Tuplet-Bracket and Slur.
The problem in the 2nd is, that the scope of the slur is too large. What can I do to make this better?
Thanks for Your help,
Stefan
\version "2.13.3"
firstVoice = \relative c''' { a2 ~ ( a8 f aes ges) }
secondVoice = \relative c'' { \times 8/9 { b16 [ ( cis c ~ ] c[ d e~ ] e[ ) b ( cis] ) } c8 r8 r4 }
% first snippet, collision between TupletBracket and Slur
\new Staff { 
<< {\firstVoice  } \\  
 {\secondVoice } >>
}
%second snippet, also a collision, and a bad looking slur
\new Staff {
<< {\firstVoice  } \\ 
  \override TupletBracket #'padding = #2
\once \override Slur #'positions = #'(0 . -10)
  %why does the slur here have such a strange look?
 {\secondVoice } >>
}
%%%%%% end of all snippets %%%%%%%%%%