Sorry for my earlier post stating the obvious - I hadn't read the full thread. Having read the full thread, a few things come to mind:
WWg (except S) cannot contact a fortification - no problem there, the WWg is S (p33 - note the WWg cannot contact the tower)
WWg (except S) cannot shoot from front edge if they moved - no problem there (yet) - page 34
Art can shoot from any edge when manning a PF so the Art does not need to turn (if it shoots at all)
Art and single rank of Bw can shoot from a PF (p 34)
You cannot move a group into corner contact with an element defending a fortification (p33) - have you moved into corner contact? If so, the WWg must use up to 80 paces of free slide (p33) to end in front edge combat with the Bw otherwise this is an illegal move. The single Bw element doesn't conform to the group in this situation (p33). If this is not in contact (a corner is not an edge - commentary p29) then no slide is necessary because the elements are not 'not lined up' nor TZ-ing eachother and the WWg assaults the PF, and the Bw does not provide overlap support to the PF.
In any case, the Bw cannot slide 80 paces to get into combat when defending a fortification (must be less than 80 paces - see page 42) so the whole corner to corner question requires no clarification.
Now the WWg is in front edge combat (see below), nothing shoots at either the WWg or Sp (p34).
If the Bw was not there, is the WWg in close combat? Some say yes, some say no. The PF has a combat factor so by deduction the answer is yes, despite the rules saying you move into front edge contact with an enemy element (which a fortification is not - p11). Consider then this scenario : you move your single elements front edge into a full legal flank contact with an enemy single element. The enemy conforms after shooting and you have a Bw that could shoot at that enemy. Can your Bw shoot at that enemy before he turns to face? It has nothing in contact with its front edge (nor did it move its front edge into contact) so the enemy element isn't in close combat is it? But if your opponent also has a Bw such that the element you just moved is in his range, he cannot shoot at you given you are in close combat. But against what? By deduction your element is in combat with the element that has not yet turned to face, so is shooting allowed from either Bw in this case? Consider the can of worms it will open if your Bw can shoot at the enemy element where you are in flank contact. In other words, shooting is not allowed in this situation. I believe the same logic / deduction can be used when assaulting fortifications - just my opinion!!
Cheers
Andrew