Printing titles at a consistent size

[David Sumbler]

My current project is a quartet.  The score and each of the 4 parts are
in separate \book blocks.

I have #(set-global-staff-size 16) before the score \book, and
#(set-global-staff-size 20) before the first of the 4 part \book blocks
which follow.

Today I turned my attention to formatting the titles etc. which come at
the top the first page of each book.  Because I did not find the default
layout very satisfactory, I decided to rewrite 'bookTitleMarkup' (using
the default in titling-init.ly as a starting point), and my version is
now included in a global /paper block before any of the /book blocks.

Of course, I then realized that the different staff sizes between the
score and parts affects the titles also.  I was able to restore the
titles in the score to the size I want by adding '\fontsize #2' to each
of the title items.  So far so good.

However, after a lot of experimenting I have not found a way to increase
the baseline-skip value just for the titles in the score.

Perhaps someone can tell me how to achieve this.

But is there perhaps a better way of getting the titles to appear the
same size in the score and parts, despite the different staff sizes in
the music that follows the titles?

David