Form what I observed, Object-type MCDs stop units from spawning in the tiles containing them, ignoring if the Object itself blocks movement or not.
This seems fine, but becomes an issue for xcom crafts. To close LOS "holes" in the wall (in places where the wall changes from straight to oblique) you have to add small "edge" Object-tiles.
Normally you place them internally (vanilla UFOs do this, see U_BITS terrain), but they block xcom units from spawning (even if they're walkable-flyable-slideable) in the tiles where you placed them.
So I placed them externally, but they paint black the tile (floor included, even if no floor tile is placed there; see screenshot) and this "black floor" doesn't seem to go away even looking directly at it.
I don't know how to fix this.
Removing the landing gears and placing the whole craft body to floor 0 *could* (haven't tried though) fix the black floor; but I love my Ramp of Death™.
Another way to fix this of course is to not use oblique walls...
Lightning craft puts these "gap filling" MCDs both internally and externally. But the tiles they're used in aren't marked as spawnable so no spawn-blocking issue; and they are see-through, so no "black floor" (but you can also see through Lightning's oblique walls, which is quite bad).
Any idea?
Would it be problematic to check for movement-allowing of Object-tiles and make them spawn-able? There's always a "Target_Type: X-COM" floor MCD under them. In UFOs and others hostile crafts the thing is obviously never an issue, because the units aren't spawned packed altogether like in an x-com craft.
(I'm using OXC Extended, but I don't think this is a problem specific of that version).