The current bar number default position is fine for bar numbers at the
beginning of the line but not for bar numbers placed on every bar or
every n bars. When bar numbers are placed every n bars they appear to
the right of the relevant bar (I guess this is to avoid collisions with
the clef symbol when bar numbers are only at the beginning of the
line). I suggest that slightly different logic should be applied when
\set Score.barNumberVisibility = #(every-nth-bar-number-visible <n>) so
that the bar numbers at the beginning would be consistent with the rest.