Avoiding tie/prall collision

[Helge Kruse]

Hello,

I have some measures with similar rhythmic pattern but different pitch. 
But all look similar like this:

\context PianoStaff <<
  \context Staff=right \relative c'' {
    \key g \major \time 3/4 s2. \stemUp
    d4~ d16 a' g\prall fis e\prall d cis\prall b | % 33
  }

  \context Staff=left \relative c' {
    \key g \major \time 3/4 \clef bass s2. \stemDown
    \change Staff=right r16 a' g\prall fis g4 \change Staff=left r | % 33
  }

>>


Every time I get a collision between the tie and the prall ornament. I 
already changed the tie to "d4^~ d16" but the \prall is still above the 
system. What is the best way to move the prall ornament below the tie?


Regards,
Helge