Alot of the time the difference between square and border is wall size. For instance, if it's a building giving you cover, then it's the square. Where as if it is just a wall justting out, not the entire 5-foot square, then it would be the border.
About the corner ranged attacks against melee, yes this does allow a non-modified attack without an AoO, but this is also one of the perks of ranged combat. Ranged often deals less damage, suffers from smaller cover than melee (if melee'ing over a fence there's no cover, if shooting there can be), firing into a melee (can be offset by a feat, but still), and last but far from least AoO with every shot if someone is in melee. If your getting into physicality, I think this would make sense. It's much easier to shoot around a corner than swing a sword past one.
And one last tid bit, what are the chances that melee opponent is in melee with a party member (e.g. Valeros in the diagram with the ogre), that is a -4 right there, why give them technically a -8.
About the corner ranged attacks against melee, yes this does allow a non-modified attack without an AoO, but this is also one of the perks of ranged combat. Ranged often deals less damage, suffers from smaller cover than melee (if melee'ing over a fence there's no cover, if shooting there can be), firing into a melee (can be offset by a feat, but still), and last but far from least AoO with every shot if someone is in melee. If your getting into physicality, I think this would make sense. It's much easier to shoot around a corner than swing a sword past one.
And one last tid bit, what are the chances that melee opponent is in melee with a party member (e.g. Valeros in the diagram with the ogre), that is a -4 right there, why give them technically a -8.