At the Equinox (coming soon) on the Equator, the Sun is vertically overhead. At the North Pole the Sun is at a constant angle of about 23.4 degrees above the horizon at the North Pole. I think this is consistent with both RE and FE models, but do correct me if this is wrong.
On a flat Earth, simple trigonometry says that the height of the Sun is about 0.43 of the distance from the Pole to the Equator (tan(23.4)~=0.43). If that distance is 10,000Km then the height of the Sun would be about 4300Km.
Is this roughly correct? I am clearly taking this angle from data generated from an RE model of the Earth, so that may be the problem, but a similar calculation could be done at any latitude as long as the measurement is done at the highest point (noon).
I am aware that the theory of Electromagnetic Acceleration would give different figures but (according to the WiKi) this is not a complete theory and there is no experimental evidence for it. When there is an experiment that can measure light curving upwards then we can use those results to adjust the figure I calculated.