"If the world was indeed flat the measured angle to any star would remain the same no matter where you were on the flat world. Because the globe is actually round the measured angle to any star changes as you move towards or away from it. For example the angle to the north star gets smaller (in relation to Horizontal) as you go further south. This would not happen on a flat world. This is just basic geometry stuff."

Hang about a minute, if you have a “relatively” fixed point in space, such as a star, and the angle to it is measured between a point on a flat plane (the earth if it was flat) and that star, then, if the point of measurement on the flat plane is shifted, then the angle measured to that star WILL be different.
Any way, sailers only needed to “navigate” across the seas centuries ago because they couldn’t afford the tickets to fly with Quantas.?