In the earliest days of the game, repose was added, and at the time it
seems that the intent was to have nodes "roll" off of their perches.
This caused problems though with tree leaves wandering an unlimited
distance down grassy hillsides, so it was changed so that repose
nodes could only roll off of loose/falling nodes that were able to "tilt"
to let the above nodes come off. Because of this, the implied action
here seems to have changed from "rolling" to "sliding", so the extra
ceiling clearance is no longer necessary.
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