What thepurist said, the curvature of the earth is measurable over things as small as two hypothetical skyscrapers over the road from each other being further apart at the top than at ground level. But they have to be hypothetical as they’d warp in the sunshine and wobble too much in the wind to actually measure it, but you can put a number to it in the order of millimeters. So it is worth at least thinking about whether it’s worth calculating.
The curvature of the earth is about 125mm/km (obviously 2km is more than 250 because it’s a curve), but you’re only talking 20 ish feet over 28 miles, relative to your “approximately 40,000”.
Related fun fact – particle accelerators are built “flat” because you’re trying to observe a particle (which should be affected by gravity) that’s behaving like a wave (which isn’t, not at this scale or frame of reference anyway).