bar number interference

[bb]

The bar number is just above the 7 of the fis2:min7 and makes  the chord
name unclear.

How can I avoid this? How can I generally (always) set the bar number
directly above the bar line by default?

Snippet:

\version "2.18.2"

melody = { \override Score.BarNumber.break-visibility = ##(#t #t #t)
\time 5/4   b2.( b4 ) r4 | }

harmonies = \chordmode { b2.:min fis2:min7 | }

\score {
<<
  \new ChordNames { \harmonies }
  \new Staff { \melody }
>>
}


Kind regards BB