A little help

[Rip _Mus]

Hello everyone,
I have prepared a minimal example (attached) to explain my problem.
In a PianoStaff, transiently, I insert a new staff above the left hand to
create a kind of "tactus" reference (widely used in contemporary music).
I wonder how I can do to decrease the excessive distance between the
extreme staves, in order to make everything more compact.
I'm looking at the chapters related to vertical spacing, but I just can't
get out of them.


Thanks and greetings to all

Rip_mus

\version "2.22.1"

su = \new Staff = "su" {
  \relative c' {c4 d e f}
}

giu = \new Staff = "giu" {
  \relative c' {
    <<
      {b4 a g f}
      \new Staff \with {
        \remove "Time_signature_engraver"
        \remove "Clef_engraver"
        \remove "Staff_symbol_engraver"
        \override NoteHead.stencil = #point-stencil
        alignAboveContext = "giu"}
      {c'4 c c c}
    >>
  }
}


\score {
 \new PianoStaff <<
 \su
 \giu
 >>
}