The noteheads of whole notes are considerably wider than the noteheads
of smaller value notes, but a whole note harmonic has a notehead that is
exactly the same width as a harmonic notehead of any lesser value, and
considerably narrower than the head of a normal whole note. This makes a
whole note chord look rather ugly when one of the notes in the chord is
a harmonic. For example, here is the final bar of Villa-Lobos' Etude No 1:
\version "2.17.25"
\relative f'' {
\key e \minor
<<
{ \override NoteHead.style = #'harmonic-mixed b1 }
\\
{
\set tieWaitForNote = ##t \stemUp
\grace { e,,,16~[ gis'~ cis~ e~] } <e,, gis' cis e>1
}
>>
}