In a Couple Box I have an empty birth field but the baptism details are not substituting into that space.

I have gone to Preferences > Fields > Person Events > Birth and selected 'Baptism' in the bottom box ('If no birth date exists, substitute ..') but the baptism does not appear in the couple box (although it does when that person appears in the Children field!).

Would love to know what I am doing wrong / haven't done.

Should this substitution request also apply to the full database or only the couple open?

Many thanks
Elizabeth