hmm…
That’s like saying AA should only defend from aircraft that are coming from a certain direction… I disagree with the concept personally.
The theory is that the mines EXIST, and are deployed as per the next expected engagement as an auxillary to the defending troops in the region exactly like AA units. Things benefit from being expanded, yet kept simple.
It’s the same reason your troops defend the entire territory and not just one border.
Options for minesweepers/combat engineers is cool. Again, great if we’ve got pieces, not so great if we don’t, rules should be setup in a way that these kind of options can be added, but not so that they are required.