Rhythmic independence between two voices is measurable and should gate open-score recommendations, not just pitch proximity

Homorhythmic writing (chorale-style, both voices attacking together most of the time) tolerates close tessitura and even brief beam proximity because the ear and eye track the two lines as one texture. Independent counterpoint (fugue, invention) does not get that benefit, so much lower thresholds of proximity or crossing already read as confusing.

Treating a fugue exposition with the same tolerance thresholds as a chorale — this is why the BWV 847 case tangled with zero pitch crossings: the voices' rhythmic independence, not their pitch relationship, was the actual driver.

Stone, Music Notation in the 20th Century (independent-part notation).

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.