The answer is really interesting: The Inmarsat satellites are not in a geostationary orbit, but only in a geosynchronous orbit. They don’t orbit the earth along the equator, but on a slight tilt. So what happens is that the elevation changes slightly - up and down during the day. That pattern is actually a figure eight that is very narrow called an analemma. Geostarionary satellites are a special case of geosynchronous satellites. Their orbit is aligned exactly with the equator. They appear at one spot.
You can see the orbital position of the satellite carrying Outernet over the Americas here.
Notice it’s higher up in the sky at night and then lower during the day.