Oh?
Since "Major" is defined as "slightly narrower than a single Form", and a tunnel allows any and every Form to be cast down it (dependant only on Range:Touch)... you really think it suggests that? 
Yes, I think your post suggested it. I don't believe it's the case, nor do I believe that you believe it's the case. Simply stating, it's not a legitimate magical focus would have been better.
I find the Socratic method better when possible. Show the logic to finding the answer, instead of the answer itself.
It's the lack of that logic that would make one believe my first post suggested it was a Major virtue.
Yet you very specifically limited the inquiry to minor magical foci (drawing attention to it by putting it in quotes), when you could have easily asked if it fit within the bounds of major or minor.
Actually, logic leaves two possibilities if the proposal isn't a minor focus; it is either a major focus or it is not a focus. The context of the discussion, being about foci can reasonably lead the reader to conclude that you think it is a major when you specifically limit the inquiry to minor foci.
I really liked a character I did with specialty in creating stone/metal structures. She had spells for temporary stone huts, soaring wizard towers, bridges, even a full village with paved roads.