Vertically centered refrain

Hello,

I have a song with an even number of stanzas. I want to have the refrain 
in the vertical mid of all stanzas. In this case it's necessary to move 
the text in one verse up or down. It would be preferred to find an 
automatic calculation to find the best location, but I tried at least a 
manual adjustment. Unfortunately it works only with the characters, not 
wit the hyphen. How can I make this better?

Regards, Helge

\version "2.26.0"

melody = \relative c' {
   c4 c c c  c2 c c c
}

verseI = \lyricmode {
   this is verse one
   {
     \override LyricText.extra-offset = #'(0 . -1.3)
     the re -- frain here
   }
}

verseII = \lyricmode {
   this is verse two
%  { the re -- frain here }
}

\score {
   <<
     \new Staff <<
       \new Voice = "mel" { \melody }
     >>
     \new Lyrics \lyricsto "mel" { \verseI }
     \new Lyrics \lyricsto "mel" { \verseII }
   >>
}