Why would the convergence of two lines depend on where you were or what your orientation is, unless of course you are secretly accounting for the disappearance due to the Earth's curvature?
The broadness of the perspective lines constitutes your vanishing point. The vanishing point occurs where the perspective lines are less than one minute of a degree.
One perspective line lays along the surface of the earth and the other perspective line is at the level of your eye. Hence, this creates an angle into the far distance.
When you increase your altitude you are changing your eye level, pushing your vanishing point backwards, as you climb in height, changing the broadness of your perspective lines in relation to the surface of the earth. Thus you can see farther before the vanishing point occurs.