1) No matter what the terrain is, no matter what the narrative nor how creative the players are, the rules specify that the defender chooses the defense zone (baring GtA of course). If you are playing a scene where some TIEs can only fire at their target's Aft zone then you aren't following the rules.
2) This is a case where the rules are actively working against the narrative. Which is precisely the point of this thread. Why have rules that seem to support narrative gameplay but actually work against it?
1) Well, in one way you're right, but it's a very inhibiting perspective, with a very simplistic view on gaming, the rules and space combat. There's always what some call rule 0. I mean, if the rules becomes this framework within which you must rigidly fit everything, you're doing it wrong, there's nothing wrong with the game. Also, there might be upcoming products that flesh out more on the use of terrain in space battles, which could adjust the rules. Of course we cannot implement non-existent material, but to ignore the possibility and create ones own solutions to this isn't breaking the rules (not that it matters really, if you think it is) it's adapting the rules and the game to fit the narrative, which is the whole point of roleplaying - in my book anyway.
2) The rules don't work against narrative gameplay, how is that even possible, with some creativity and autonomy you use the narrative to inform the rules, the rules to inform the narrative and you improvise and go with what makes sense. For instance, a starship that has it's whole front end hidden inside a form-fitted hangar bay cannot be hit in the forward defensive zone, regardless of your reading of the rules, because simply it doesn't make sense. To argue that it should be possible is leaving reasoning at the door before entering the game.