I have a clear view of the ocean to the west, but hills at 5 degrees up to the South and 2.5 degrees up to the North. East, where I get almost nothing, is more like 15 degrees up.
I have gotten 298NM to the west, which is straight out to sea, but am nearly blind the east, due to hills. South I only get 70NM and North a little over 100NM, all due to hills.
My antenna is about 183m above sea level, so my visible horizon out to sea is about 27NM. I did have my antenna 30m lower, and the range was almost the same. I only lose a few NM to the horizon at 155m, so the dominant issue for me is the hills.
The aircraft altitude gives it the range to reach me. An aircraft at 40,000ft would have a visible horizon of about 220 NM If the signal skims to sea, I should get about 247NM range (my 27NM + the aircrafts 220NM). I actually get quite a bit more, depending on the atmospheric conditions. I'm currently getting only about 270NM. It jumps up and down with the weather.
I looked up this location, and it is only 10m above sea level, so the land around their station must be pretty flat for a considerable distance.