\version "2.18.2"

\new Staff \relative g' {
  << g1 s1\sfz >> % 1: sfz attached to spacer too far left
  \revert Script.self-alignment-X
  << g1 s1\sfz >> % 2: correct position after revert
}

\new Staff \relative g' {
  << g1\sfz s1 >> % 3: sfz correct when attached to note instead
  << g1 s1\sfz >> % 4: sfz too far left as in no. 1
  g1\sfz % 5: sfz correct when no spacer involved
  << g1 s1\sfz >> % 6: sfz attached to spacer now correct
}