grace note stem lengths

[Kevin Barry]

Dear LilyPond users,

Occasionally I find the stem lengths of grace notes to be too long, as 
in the following example, where the grace 32s have longer stems than the 
normal ones (because of the slope I think):

\version "2.16.2"

\relative a' {
  s  a32 \afterGrace a { b32[ g] } a8
}

I have tried to alter them with various overrides, including
\override Stem #'(details beamed-lengths) = #'(2)
but they mostly have no effect.  Only
\override Stem #'length-fraction = #0.5
sometimes works for reasons I don't really understand (the behaviour of 
this property seems unpredictable - different values have odd effects) I 
gather it's not for this purpose, but I was just trying everything I 
could find in the internals manual. Could anyone shed some light?

Kevin