Speed Index 3.8 -> 1.9 with LCP unchanged at 2.0s

Speed Index 3.8 -> 1.9 with LCP unchanged at 2.0s
Speed Index measures how fast pixels fill visually; you can have a good LCP and a bad SI.
— LCP element painted at 2.0s, but the rest of the viewport stayed blank until 3.8s (staggered hydration)
— Skeleton screens filled the visual area progressively: SI 3.8 -> 1.9
— Perceived speed improved even though the single LCP number didn't budge
— SI weights early frames heavily — painting *something* across the viewport early wins
Takeaway: Speed Index 1.9 — fill the viewport early, LCP isn't the whole picture.