Tall bars in two-line music

[David Wells]

Hi,

I'm working on typesetting some chants with two lines per staff and the 
resulting barlines are too tall. Tiny example:

\version "2.24.3"

\score
{
\relative c'
{
  \time 9/4
  \slurDown

  \override Staff.StaffSymbol.line-count = #2
  f4(g) a f(g) a(g) g2 |
  f4(g) a f(g) a(g) g2 |
  \break
}
}

output:

Here, I expect the barlines to be the same height as the staff (i.e., not 
protrude) and I cannot figure out how to make that happen.

Interestingly, if I add a lot of lines to the staff then the bar is lengthened 
correctly - the problem seems to be that it is too short.

Best,
David