I could have sworn that there was an example in the manual of how to prevent an entity from taking additional ambient light based on the ground's own light value. (In fact, I thought this was exemplified by an airplane flying over terrain, but a search for that didn't turn up anything.) I don't want to use .unlit, as that would (presumably) prevent the entity from being lit by other light sources. Can someone point me in the right direction?

I'm assuming you are referring to the FLOOR_RANGE variable. I guess you could set it to 0, but this will effect all entitites and not just an individual one.

If you only need it for some entities, then you can probably have the ones that need it use an action that:

1.) Stores their real albedo and ambient in a skill.
2.) Trace down to the floor.
3.) If the trace distance is under a threshold, use the tex_fog/tex_light values with the albedo/ambient skills, and compute the real albdeo/ambient's for the model.

If you get to the point where you are doing to many traces, then you could save the position of the entity each frame, and only trace when the entity has moved.

That's just what I was looking for (and more)! Thanks much.