postlight is rendered below levels 11+

[XenonA7]

The map editor renders the following layers underneath levels 11+:
light
postlight
last
object1
object2
object3

In the images below, note how the heightmap (postlight) is rendering underneath Ground(11).

Ideally these special layers would be on top of all elevation levels. Currently it is difficult to make light maps for high elevation levels since you can't see what you are doing.