It has to do with the way they redesigned it for AC3. In order to get it to work on slanted rooftops and steps, they made a vertical tube area of effect so it actually reaches above and below now. They reduced the length of the tube, but it will still go up and down a bit and when you grab you're right at the target's feet, so they can't stop it from stunning you without removing the low side of the tube completely.
I don't see smoke bomb too much in Deathmatch, but when I do I love baiting it since its cooldown is so long now. Nothing better than rushing your pursuer and doubling back before getting smoked, then knifing them and stunning. Take a contract loss and 100 seconds until your next smoke bomb, LOL!