That has a lot to do with everything.
You just stated it all though at the same time.
The lower to the Horizon the more obstructions there are.
Tree's, Mountains.
Looking out my window 17 degrees would be right into the mountain range thats only 1/4 from my back yard. Impossible to get a signal, unless someone calls a blasting crew.
If every Satellite was 90 degrees up Line of sight would never be an issue, But That most likly impossible.
Since they have to be over the equator,and it can never be 90 degrees for everyone.