Here is a vid that shows the same part of the earth. The observer is 30 miles inland from the shore (with a known height) looking out at the mountain with the windmills in the foreground. The geometry of a flat earth would put the mountain 3 times higher than what actually appears. This is the part of the mountain hidden by the curvature of the earth.
RE: BLACKPOOL TO ISLE OF MAN, EARTH IS FLAT, CASE CLOSED! #FLATEARTH