I've noticed that some of the medical beds won't allow you to have NPC's lying on them. Normally I set the NPC "Y" coordinate for 1 meter, which works well.

Sometimes, however, the NPC's end up lying on top of the covering of the closed bed, or hovering over the open beds.

The covering of the closed bed or the partially raised sides of the open bed shouldn't be the reason, or you wouldn't be able to put one item inside another, or place an item so it ends up sticking halfway out of a wall or floor.