I've said it before, and I'll say it again. One of my favorite aspects of this game is that it ecourages player interaction and agreement on the sometimes ambiguous aspect of play, this question being a perfect example. In my opinion, it is a far more "human" game than anything out there. You have marginal errors on movement, jostling other ships during movement or measurement, inexact placement after overlap, judgement calls on range and firing arc. It comes down to an agreement between the players about which way it goes, and I think that this interaction is what sets the game apart, rather than relying completely on the ruleset to solve every equation. Absent a gentleman's agreement, for our group we usually call in a third party for an opinion, but there have been times where we've used the rolloff as well.
It is interesting to see Parakitor's take that perhaps a "tie" should go to the attacker. IMHO, the attacker already has the advantage on the dice, and I'd like to point out that in some of FFGs card games (yes I know it's a different medium but I'm looking at precedent here), a tie goes to the defender. In AGoT challenges, ties in strength go to the defender. In the Star Wars card game, Edge battle ties go to the defender, and in the Force Struggle a tie means the Balance token remains unchanged, which in my book is a victory for the "defender".