I have been flying for 10 years and I do not see any curve

How much does a fisheye curve

Flat.

According to google

Using the Pythagorean theorem, that calculates to an average curvature of 7.98 inches per mile or approximately 8 inches per mile (squared). The distance to the horizon in miles from height of an observer is approximately equal to 1.23 times the square root of the height in feet.

It depends how much you see

http://earthcurvature.com/

I have no idea then