Consider the very example you shown on description, it goes to the right, then to the bottom.
But what if i want it to get to bottom first then goes to the right ?
I don't get how it determine the behavior (on placing wall; even with no obstruction).

Consider this scenario, i often want to use the cliff/lake/river as part of the wall; where the wall is still follow the same tiles after partially being cut away by some obstruction.
But this mod avoid that path (for obvious reason)
I wish there is a way to force the path.

You have a good question!
I thinked about that too when i was making the mod...
Find a random path, if can't build in this area, then check the other side.
And if i want to make it underground?
And if i don't want to use the other side?
And if i find a real path? Like a spagetti? (I think it's hard, but it's possible)

Then i thinked about the easy way to do it, just make 2 lines and 1 curve (If i need it)
I divide the area in 4 sectors, north, east, south and west

(If you have problems in 45%, try to do a tiny path)

I think it's the best way, with a bit of practice, it make very easy to build

/deleted, please ignore/