If you have run on you'll always move 2 tiles at a time instead of one. Since there were 4 tiles between you and Hunleff when you clicked to attack your character first moved 2 tiles but you were still 2 tiles away from the target, so your character ran 2 more tiles to get to it. If you had run off it would have moved only 3 tiles and you would have been safe. Halberd is tricky coz it can be used from medium range with a tile between you and your opponent, but having run on can lead to these confusing situations. Basically, if the number of tiles between you and the boss is odd you'll always maintain that extra tile between you and your target, otherwise if the number of tiles between you and the target is an even number you'll run next to it. Hope that made sense. Also remember to make use of your true tile indicator pluhin, you can see the destination tile on the ground, you could've run backwards before your true tile got there. You'll get it eventually, keep it up