Færder fyr/lighthouse Nikon P1000

The hight of the tower is 47 meters above sea level. (https://snl.no/F%C3%A6rder_fyr)
I filmed from 19,5 km away, 1 meter above sea level. (Østre Bolærne)
Using the https://earthcurvature.com/ calculator, 30 meter should be below the horizon.
So something is not right. The math? My eyes?
Or maybe the information we have been fed....