Tested Hells Pass with
!setoptions typemapsetting=alloff
The spiders
can cross the hill... but the pathfinder has convinced them that they can't. Order a flea to the foot of the mountain range and tell him to go to the other side, and he'll take the stupid way around through the pass. But if you hold his hand by giving him 5 waypoints over the mountain, he'll do it.
WTF pathfinder?