There was a particularly annoying -8/Materials Heavy i was trying to avoid.
Its range covered the lower path (unless i wanted to try an extreme dig), so i tried to go around and above.
But no, the Heavy sensing area covered all possible paths above as well. The upper path was worse than the lower one.
So i went back down. The most convenient path through the Heavy's area of influence was barely inside the lower part of the its field of view.
I ended up breaking the walls directly below the Heavy's sight range, to barely graze the edge of its view.
This of course directly funnels me into a squad of hostiles, but that's not important.
After all that, i get close enough to a Tunneler for it to begin digging out a new room...
One very big room, big enough to directly neighbor a room on the side of the Heavy's range i started on.
Turns out the "extreme dig" would've been an breezy two-tile dig.