I did some fiddling with the altitude table data and succeeded! On the other hand, for the heck of it, I created a field on my MIG-25P using all 1's for stages and now have a MIG-25 that disappears completely after 105,000 feet. Oops. Of course a simple nose dive brings you back into the cockpit of the plane. I take it the gaming engine only allows you to fly up to 105,000 feet or something.
Also, some pictures I have seen up here using what looks like the Siberian Sky effects (I have) in fact look like the sky is darker and closer to a stratosphere look. No matter how high I get I still see blue, but some people have almost a solid black in their screenshots. It looks like they are literally in outer space. What Environment system file is that???