figuredBassCenterOnNote = \override BassFigure #'X-offset =
#(lambda (grob)
 (let* ((paper-col (ly:grob-parent grob X))
        (elts (ly:grob-object paper-col 'elements))
        (figure grob))

   (for-each
    (lambda (idx)
      (let ((elt (ly:grob-array-ref elts idx)))
            (set! figure elt)))
    (iota (ly:grob-array-length elts)))

   (-
     (interval-center (ly:grob-robust-relative-extent figure figure X))
     (interval-center (ly:stencil-extent(ly:text-interface::print grob) X)))))

\pointAndClickOff
\header { tagline = ##f }

\new Staff << { \clef F c1 c c \bar "|."}
  \new FiguredBass \figuremode {
    \figuredBassCenterOnNote
    \set figuredBassPlusDirection = #RIGHT
    <5>1 <6 4+ 2\+> <6>
  } >>

\new Staff << { \clef F c1 c c \bar "|."}
  \new FiguredBass \figuremode {
      \set figuredBassPlusDirection = #RIGHT
    <5>1 <6 4+ 2\+> <6>
  } >>