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Misplaced enemies, why don't they get stuck?

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I've been studying the Doom engine and map internals for a while and noticed something odd. On E1M1, in the room left from the start there are two shotgun guys behind the pillars. If you look at the map in an editor, you'll notice that the distance between them and the pillars is only 16, whereas their collision radius is 20. Does this mean that they are actually stuck in the pillar? They don't seem to be in Doomsday at least. Can anyone explain to me how the engine handles cases like this where a thing is set to spawn partially overlapping a wall?

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I think they're able to get unstuck because they take a step that's bigger than the amount they're stuck in the pillar. They take 8 map unit steps but are only embedded 4 units into the pillar, so when they take a step Doom realizes they aren't touching anything at the new location and lets it go.


On the other hand, the infamous MAP02 shotgunner is embedded deeper than 8 units and trying to move in any direction means they'd still be touching the wall at the new position, so it gets rejected.

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Does this mean that if an engine implements variable timesteps, then these enemies will be stuck at higher framerates and free themselves at lower ones?

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