Melee- Melee's distance rule is simple you MUST be 1 space from your enemy to attack with melee.
Close Ranged- You must be at most 5 spaces away to use close ranged weapons to hit targets.
Mid Ranged- You must be at most 10 spaces away to use mid ranged weapons and to successfully hit targets.
Long Ranged- apart from the sniper you must be at most 15 spaces away to successfully hit targets, For the sniper you must at most be 25 spaces away to successfully hit targets.