Distance is only relative when it comes to the "articulation" as to how you justify your actions.
If the guy is at 25 feet with a broomstick and you shoot him, you better be a very good writer.
Same guy at 5 or 6 feet, the justification is much easier to assume that it was probable that you truly were in fear of your life.
Same guy at 25 feet and now he has a gun, you will once again be in a fairly easy position to justify your actions.
Bottom line, if they have the means, motive and opportunity, that is when you can act. If even one of the three is missing, it is the difference from a justifiable shooting (Self defense, the protection of others) vs. Murder...