Judging precise distances under the extreme stress conditions of a critical incident, will be inaccurate at best. In fact, you WILL be wrong!
When anyone gives you an exact distance, that means if you are off by an inch or two, you are criminally responsible? I'm not thinking so.
It is getting to be a long time ago now, but I thought my attacker, armed with a large butcher knife, was about 20 feet away when he attacked. I was so certain that I gave that in my statement. I was way wrong!
Later through the investigation, it was determined he was six feet away. Even today, years later, in my mind's eye I would still think he was, at least, three times that far away.
All that was to say, it is not an exact or even an approximate set distance. A determination of Justified Self Defense will depend on the reasonableness of your actions to be decided by others long after you, hopefully, survive the critical incident.
I hoped that helped and added to the thread.
D