Case: tuning lazy-load trigger distance from 0px to 600px

Case: tuning lazy-load trigger distance from 0px to 600px

What it did: a site lazy-loaded ads exactly at the viewport edge (0px margin), causing blank slots and missed fills. We widened the IntersectionObserver rootMargin to 600px.

— Setup effort: 1/5 (one rootMargin value)
— Outcome: fill rate on below-fold slots rose 81% → 96%, page RPM $10.90 → $11.95 (+9.6%)
— Blank-slot complaints dropped to near zero; ads were ready before the reader arrived

Pros: a one-line change recovered lost fills with zero UX cost.
Cons: too wide (1500px+) and you re-load ads users never see, hurting viewability — 400-600px is the sweet spot.

Lift: ★★★★☆ — Risk: ★★☆☆☆
Verdict: if you lazy-load at 0px you're leaving fills on the table. Best for: any lazy-load setup. Skip if you don't lazy-load yet.