dynamics contexts

[james]

Perhaps I don't understand the purpose of the dynamics context. I've been using 
them to align all dynamic marks on a single line, however, I don't see how to 
control whether the dynamics are place above or below the staff. For example:
\version "2.17.2"

\score {
   <<
      \new Staff = "tset" \relative c' { c4 b d c e d f e}
      \new Dynamics {
         \override TextSpanner #'(bound-details left text) = "text"
         s4\startTextSpan s1_\< s4\! s_\p s\stopTextSpan
      }
   >>
}
\score {
   <<
      \new Staff = "tset" \relative c' { c4 b d c e d f e }
      {
         \override TextSpanner #'(bound-details left text) = "text"
         s4\startTextSpan s1_\< s4\! s_\p s\stopTextSpan
      }
   >>
}

The former has the problem that the spanner is printed on top of the dynamics, 
and the latter has the problem that the dynamics are not aligned. Is it 
possible to get output similar to the latter, but with the dynamics aligned 
better?