Adjusting space in a lyric tie

[David F.]

How do I adjust the space between two syllables/words that are tied?  
LyricSpace.minimum-distance works for words that are not tied.

Thanks!
David

\version "2.19"

{
    c'4 d'4 e'4 f'4
}
\addlyrics {
    \override Lyrics.LyricSpace.minimum-distance = #2
    Ly -- rics with~some~ly -- ric~ties
}