Having recently fixed a similar problem with bar numbering by moving
the Mark_engraver and adding Staff_collecting_engraver at Staff level,
I've run into the following: my bar numbers are running along the
skyline of my lyrics, as shown in the fabricated example.
I like the 4 in the normal (default) position, and would prefer the
others to settle at the same level: below the upper lyrics, just above
the staff.
As before, I've arrived at 4.4.3 Outside-staff objects on p114 of
the Learning Manual (2.19.36) but, although there are default
priorities for bar numbers (and measure numbers, what's the
difference? apart from 650 in priority), lyrics are not mentioned
(as not grobs?).