Moving fingering, spacing between staves

[Knute Snortum]

In order to avoid the AB problem, what I'm trying to do is move some
fingering down in the system, but the problem I run into is I get too
much space between staves.

Here is a MWE:

%%%
\version "2.23.12"

moveFingerB = {
  \override Fingering.X-offset = -0.5
  \override Fingering.Y-extent = #'(2 . 3)
  % \override Fingering.Y-offset = -1
}
revertFinger = {
  \revert Fingering.X-offset
  \revert Fingering.Y-extent
  % \revert Fingering.Y-offset
}

rightHand = \relative {
  \oneVoice
  c''4 c c c |
}

leftHand = \relative {
  \clef bass
  \voiceThree
  \moveFingerB a8-3-1 \revertFinger f-2 a4 a a |
}

dynamics = {
  s1-\markup \large \italic "leggiero" |
}

\score {
  \new PianoStaff <<
    \new Staff \rightHand
    \new Dynamics \dynamics
    \new Staff \leftHand
  >>
}
%%%

I've attached a screenshot of what that looks like.  The problem is
there is too much space between the fingering and the markup, and this
may be because I'm not moving the fingering in the correct way.  The
X-offset works fine, but I couldn't get negative numbers to work with
Y-offset, so I tried Y-extent.  Unfortunately, I don't exactly
understand what the pair of numbers means.  It has something to do
with size, but it appears to act chaotically sometimes.  The manual
only says, "Extent (size) in the Y direction, measured in staff-space
units, relative to object’s reference point" but this doesn't tell me
what the two numbers stand for.

I'm hoping someone can explain the "extent" properties to me and help
me move the fingering without the extra space between staves.

--
Knute Snortum

fingering-staff-space.png
Description: PNG image