Can I somehow set the baseline of a walk-behind area beneath the screen (eg. at y=350 within a resolution of y=300)? Or is it possible to just don't put a baseline on the screen and say that everything - whether it's behind or in front of the object - should be hidden by the walk-behind?
You can do it via script:
In player enters screen (before fadein), add a RunScript action, then put "SetWalkBehindBase (AREANUMBER, 350);" inside.
Oh, thanks. That was easy..