Repositioning a dynamic

[Peter Toye]

I'm trying to engrave the attached snippet, and I want to make sure that the cresc hairpin is inside the slur. I assume the composer wanted the left hand to cresc but not the right hand (of course, it may be a mistake on the part of the publisher).

I tried this 

\version "2.18.2"
\language "english"
{
  \time 3/4
  \key gs \minor
  \clef bass
  \relative c'
  {
    <b fs>8\( b,\) <b fs>\(  
    \override Staff.DynamicLineSpanner.avoid-slur = #'inside ds^\< fs ds'\)\! 
    \revert Staff.DynamicLineSpanner.avoid-slur|
  }
}

but the hairpin is still outside the slur, presumably because there isn't actually a collision.

Any pointers as to how to get what I want would be very welcome.

Regards,

Peter
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