Keep in mind that once you shoot at them, they are now initiated with you, meaning they can kill you legally. YOU are not initiated with them if you only shoot at them. It's sort of a loophole to get them to shoot back at you. For example, you're mining, and you see a truck pull into the quarry. You can shoot at their tires (warning shots). However, if they don't get out to engage you, you cannot kill them. If they get out and return fire, you are free to eliminate the threat.
As for your question stated in your original post, coming up with a solution would be rather difficult, as a huge variable on Asylum would have to be altered in order to suit your personal needs. In my opinion, the rules for engagement are fine as they are. Try my "loophole" method to see if they shoot back at you before they can close the gap and stick you up. Perhaps have a friend scout for you while you mine so you can be better prepared in the event hooligans try to screw with you.
Hope this helps!