RE: Killing distance
I can understand that, but I rely on discipline as well as my brain and my gut. I've had shots at less than 20 yds. I wouldn't take, but I'm not going to limit my shooting to the least possible distance. Just this past season I had a shot at about 15 yds, but the other conditions were bad--very foggy, on top of it being darker in the woods anyway. I almost did shoot, but noticed a branch in the way just in time. Limiting myself to practicing at 20 yds or less wouldn't have changed that scenario at all.
I'm not saying you are wrong in your reasoning--as long as that is what works for you, that's great. What works for me is practicing at longer distances, which makes me more confident on closer shots, and disciplining myself to not taking longer shots on live animals.
Chad