I don't think that's true? Plasma density goes up with altitude out to quite some distance, though it's nonlinear. And in any case it's a refractive thing. H

I don't think that's true? Plasma density goes up with altitude out to quite some distance, though it's nonlinear. And in any case it's a refractive thing. Having a somewhat lower index doesn't make much difference when one lens is 40x thicker than another.