A Good Read
And to answer your (main) question, from 20/25ft. in is my zone and it's what I practice when not plinking. I believe anyone in my residence without my permission is a BG and I am prepared to defend. I have walked my house for what I consider optimum defensive positions and have "routes" prepared (hey - I spent 50+ years in Southern California and experienced a few real good rumblers so I was doing this before I owned a gun - so the transition to an armed defense was a bit easier). If I am defending my property I am already prepared to follow through if need be. But it's a call made at that moment based on the best decision making conclusions you can make in a few seconds - if more than one.
The Constitution shall never be construed … to prevent the people of the United States who are peaceable citizens from keeping their own arms. – Samuel Adams