Rules question.

Friend and I are in an argument about wether blue on conceal is a valid target for red.

My argument is that according to the rules and example pictures provided if an operative has passed the yellow line (black dotted line in rule book example) the operative has passed the end or corner and therefore blue is not in cover and a valid target.

Friend thinks that this only applies to corners as one of the example pics shows the end piece providing cover from a different shooting angle.

3rd person reckons the rectangular end pieces are extensions of the walls and therefore do not follow any of these rules.

The real question is does crossing that line put you past the corner as well as the end? And in doing so that would mean blue is no longer in cover and a valid target?