Overriding NoteHead stencil in a chord produces unwanted X offset

Hey lilypond users,
    In compiling the following:

\version "2.13.0"

\relative  c' { <c \tweak #'stencil #ly:text-interface::print \tweak #'text
#(markup #:musicglyph "noteheads.s2")  cis' g'>1 }

You'll see that the middle notehead of the above-chord is too far to the
right.  Some other tweaks:

\relative  c' { << { <c g''>1 } \\ { \override Stem #'transparent = ##t
\override Stem #'direction = #UP c'4 } >> }

Too left.

\relative  c' { << { <c g''>1 } \\ { \override Stem #'transparent = ##t c'4
} >> }

Too left.

\relative  c' { << { <c g''>1 } { \override Stem #'transparent = ##t c'4 }
>> }

Too right.

Is there anything you'd recommend that'll get this quarter note flush with
the whole notes?

Thanks!
~Mike