Smithsax, how do you know that your solution is correct? Over the years items to be highlighted in the Listener have followed all sorts of routes, not necessarily straight lines. There is no unwritten rule that tells us to choose straight lines where there is a choice.
I have been pondering this for some time and have come to a tentative conclusion. My premise is that the editors cannot possibly have overlooked the ambiguities, so there must be a way of ensuring that there is a unique solution that can be logically arrived at. I think I have seen why one solution is the intended one and the others will be marked wrong because they do not comply with the puzzle's requirements.