I went through the same struggles, so definitely know what you're going experiencing. It was especially aggravating after I had accomplished the requirements twice, only to find out I/you can't complete it in Iron Banner. Next, I was finally able to get the kills in regular crucible, without it counting as 'close encounter' kills, after researching and seeing people post that you can't aim-down-sights (not sure how much truth there is to this one though, as the opponent I killed was close enough to kill even if I were firing from the hip). Eventually, I finally got it to register (thank God). My only suggestions would be to: 1. Make sure you don't do this during Iron Banner; 2. Don't aim-down-sights, and only hip fire, to ensure they're within the appropriate proximity, of what Bungie considers to be a 'close encounter' kill; 3. Attempt this during Momentum Control, as the 'no radar' and boost to weapon damage makes it much easier to one-shot kill. Hopefully it eventually procs for you, like it did for me. Good luck!