Raising the sky dome requires knowing the necessary height. About the ionosphere.
IIRC, we start at 80kft. That's 24km, which happens to be--according to simgear/sky/dome.cxx--4km outside the sky dome. So if we bump the sky dome up to from 20 to 25km, we'll be inside the sky dome when we start at 80kft.
I just don't remember if 80kft is where we're supposed to start, or where we are starting because of the (real or perceived) sky dome issue.
