lilypond 2.7.8 bagpipe music gracenote spacing

[Graydon]

There's a fair bit of Highland Bagpipe music where a grace note occurs
between two substantial notes which are not connected by a beam.

For instance:

    \grg b8[ \thrwd d8] \dble e4 \gra e8[ f8] |

(This is the second bar of "The Green Hills of Tyrol".)  The low a
gracenote comes out much closer to the second e then the first e; it
would be much better if it were right between the two notes.

This happens quite a bit, with various notes - A4 \grg A4 shows up
elsewhere in that same tune.

What I'm having trouble figuring out is how to haul the grace note to
the left; inserting more space isn't desirable, there's plenty of space,
I just want to more-or-less center the grace note in it.  (It's better
but not ideal inside beams, such as 

b8[ \grG a8]

The grace note comes out closer to the second note than the first, but
not as close to the second note as in the 'no beam' case.

Any suggestions for how to center up these grace notes generally?

Thanks!
Graydon