The reason why I believe that the kukri is on the armour itself and not the right shoulder is because I think every Emile fan wanted to use that knife. Now you see where the knife is located that particular spot is where you would take the knife out and put it back in when you assassinated another player, in halo reach that is. I don’t really pay much attention to if that stays the same in halo 5 but I think it will work with the new assassination animation coming.
Tldr; the kukri is where it is to make you think you are using it in assassinations.