Staff-to-staff distance must grow per system to accommodate whatever is drawn between the staves in THAT system — not a fixed constant across the whole piece

The gap between two staves is not uniform across a piece; it must expand in any system where content between them needs more room than the piece's baseline gap provides — computed per system via a skyline (top/bottom envelope) comparison, not a single global constant.

This is the modern engraving-software consensus algorithm: LilyPond's system-system-spacing/staff-affinity vertical-skyline packing, and Dorico's equivalent automatic vertical spacing, both compute inter-staff gaps per system from the actual engraved content's envelope; Gould and Ross both state the underlying principle without prescribing the specific packing algorithm.

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