Why your 'good' p75 LCP still loses 18% of sessions

Why your 'good' p75 LCP still loses 18% of sessions
p75 means a quarter of your users are slower than the number you celebrate.
— Site reported 2.4s LCP at p75 — green in CrUX.
— Pulled the histogram: 82% under 2.5s, but the slow tail ran 2.5s-9s with a fat bump at 4s.
— That bump was users hitting a cold edge cache in one underprovisioned region (28% of traffic, 0% hit ratio there).
— Adding a 2nd edge POP in-region: that segment's LCP 4.0s -> 2.1s, lifting overall p75 to 1.9s.
Don't optimize the median. Find the bimodal bump in the histogram — that's a fixable segment, not noise.
Takeaway: 18% of sessions lived above 2.5s despite a green p75.