A tie arc crossing a staff line must bulge enough to read as a single clean crossing, not clip the line at a shallow angle

A tie between two notes on a space, when its arc must cross a staff line to connect them, should cross that line cleanly rather than running nearly parallel to it for a long stretch.

A tie between two notes both close to a staff line renders nearly flat, running along the line for a significant horizontal distance before finally crossing it.

Gould, Behind Bars, ch. 'Ties and slurs', tie-shape conventions; Read, Music Notation on tie placement near staff lines.

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