dynamic padding struggles

[Kieren MacMillan]

Hi all,

Can anyone explain why the following snippet

\version "2.15.8"

\paper { ragged-right = ##f }

\relative c'' {
  \dynamicUp c4 c'\mp c,
  \override DynamicText #'X-offset = #-12
  \override DynamicLineSpanner #'Y-offset = #0
  \override DynamicLineSpanner #'staff-padding = #2
  c'\mp
}

doesn't do what I want: Force the dynamic to drop towards the staff (between 
the notes, and below the skyline of the note to which it's attached) but 
maintain a minimum padding between the dynamic and the staff.

Despite trying many things, I can only seem to get one (drop) or the other 
(padding) but not both.

Thanks,
Kieren.