OK...
The circumfrence of the earth is (in 'round' numbers) about 21,600 NM (360 deg * 60 NM per deg). Divide by 2*PI, and the radius is about 3437.746771 NM.
At 36,000' (6 NM) altitude, the ratio of ground speed at altitude to at the earth's surface, IF it is calcualted on a radial arc, is 1.001454441. So, at 500 KTAS, the difference would be 0.7272205 Knots (approximately).
That said, I have no clue as to whether such a correction is built into the software. OTOH, distance covered over the ground would be LESS, not MORE, than distance through the air -- you have to fly farther at the higher altitude to get across the same number of latitude lines -- so your "ground speed" at 500 knots True AirSpeed would be 499.2727795 knots (approximately).
