It turns out that anything at 400.000 meters and above are not rendered at all on region maps. When building sky boxes, keep this in mind and do not build too low.
I have a few more tests that I am carrying out. I’m looking into transparency, as well as what happens when two prims at the same position/size overlap. I’m looking into depth as well. If a prims center is 400 meters or above, and it’s thick enough so the base is below 400 meters, then will it show on the map? My guess is no – but I’d like to verify. Any reason to this? Not yet. Just playing around in the air.