Why can the same Kp mean different chances in different places?

Answer: Latitude still matters

Latitude still matters ✓ — Correct! Kp gives a general picture of geomagnetic activity, but it does not place every location under the auroral oval. Places farther north are naturally closer to the usual aurora zone, so they need less expansion to see activity. Places farther south need a stronger event. That is why the same Kp can mean “likely visible” in one place but only “small chance on the horizon” in another.

City size matters more — Wrong. Large cities do not change where auroras occur. What big cities often do have is stronger light pollution, which makes faint auroras harder to see. That affects visibility, not the aurora zone itself.

Air pressure sets the zone — Wrong. Air pressure matters for storms and everyday weather patterns, but it does not define where the auroral oval reaches. That depends mainly on geomagnetic conditions and latitude.