So you can "lock on" with the knife on a prone dude when you are standing but it seems harder. I dragged a sniper right up off the ground and slit his throat. Only problem was his buddy also prone 2 feet away. Also I got his default tag plus his "Mass Effect 3" tag under taken and now it gave me 2 "melee kills" not one, at least in some stats like my sig. Guess they need to fix that but I'll take it as my crash cheated me out of one yesterday!