If the tank can see the mobs to mark them, you can see the mobs to target them. I always have the mob marked for me to trap targeted before the pull. That way there's no confusion, mistargeting, or unnecessarily delays. I can stand where the tank is when he/she is marking, target my mob as soon as the mark goes on, and then run back to where the fighting will be. As soon as my mob is in sight after the pull, shoot, draw it into your trap, and then use your assist focus macro to lay down some dps as appropriate. Good Hunters tend to be very mobile in groups. It just doesn't work to hang back with the casters and wait until the pull has happened to get organized and squared away for the trap.