FWIW, that particular problem isn't likely going to be an issue for Starlink. Starlink satellites orbit at 550km vs. 20000km for GPS. The transmission is much (much) closer to a straight line approximation and ionosphere refraction is negligible.
In fact, the line of sight transmission to and from a Starlink satellite is likely to be significantly better than that between an airliner and its local WAAS station, which is confounded by ground reflections. (Edit for clarity: WAAS is just digital data, this isn't an actual error in the signal. The point is more "you have to spend more engineering effort on the transmission environment of the correction signal for GPS than you do on the actual signal for Starlink")