even more proportional, even colliding with first Clef and Time Signature?

[padovani]

The proportional section of the manual and this snippet
https://lsr.di.unimi.it/LSR/Item?id=230 are great, but I would like to have
proportional notation also in the first measure (even if this creates a
collision with the clef). Is it possible?

I know it may seem strange, but it would be useful in a chronometric
transcription I'm working on in which I may need to have Clefs and Time
Signatures in some points (and so I cannot just remove the engravers)

Below is what I am trying (I would like to make the first notes to collide
with the first Clef and Time Signature of each Staff).

Thanks for any hints!

\version "2.24.4"
\layout {
    \context {
        \Score
        \remove Separating_line_group_engraver
        \remove Forbid_line_break_engraver
        proportionalNotationDuration = #(ly:make-moment 1 16)
        \override SpacingSpanner.uniform-stretching = ##t
        \override SpacingSpanner.strict-grace-spacing = ##t
        \override SpacingSpanner.strict-note-spacing = ##t
        \override Clef.outside-staff-horizontal-padding = 0
        \override PaperColumn.used = ##t
        \override SpacingSpanner.shrinkability = #infinity
    }
    \context {
        \Staff
        \remove Separating_line_group_engraver
        \remove Forbid_line_break_engraver
    }

}

\score {
    \new StaffGroup <<
  \new Staff {

    c''8[ c' \clef alto c' c' \grace { d''16 } c''8 c'] c'4
    c2 \grace { c16[ c16] } c2
  }
  \new Staff {
    \tuplet 7/4 { c''16 c'' c'' c'' c'' c'' c''} c'' c'' c'' c'' \tuplet
3/2 { c''8 \clef bass cis c } c4
    c1
  }
    >>
}