Buckle arrow \"Kill enemies from behind\".How to perform? (Red Dead Redemption 2)

I can't figure out how to upgrade this buckle? Shot in the back of fleeing enemies - does not count, tried to stand with his back to the enemies and shot them from a turn - does not count. He sat on a horse with his back to the enemies and shot, does not count. How to kill from the back? I can understand how it is pumped?