An articulation mark whose notehead sits ON a staff line must clear that line, not sit on top of it

When a note's notehead is exactly on a staff line (not a space), the articulation mark placed close to the notehead must not visually merge with the staff line itself.

A staccato dot on a line-positioned note (e.g. B4 in treble clef, the middle line) renders so close to that line that the dot visually fuses with it.

Gould, Behind Bars, general spacing conventions; SMuFL staffLineThickness gives the line's own thickness as the floor for what 'touching' means.

This rule is about where marks land on the page, so it can only be judged after engraving. Collision and spacing faults live here.