self defense heavy bag

As I use the bag for fitness..............would the approach to hitting the heavy bag be different than a boxer using the bag. I never will box but I love the bag..........I am hitting the bag with form and concentration ........improving my endurance with running. It is really working........I love it. Because I will never competitively box, I would welcome any good practice for self defense............in a confrontation.......... I feel like staying off of the ground and having endurance to continually swing if you are in good shape will take care of most because most people because they aren not in shaphe..............they couldnt hit a bag 1 minute or run a half mile withouth puking............I have heard speed kills........I am lanky at six 1...185........not skinny as I lift light weights and run all the time. Good shape for my age at 43 In a street confrontation.........my bag practice has made me confident.......I have been sucker punched and knocked out for a second or two in a bar fight before.........that will not happen again if I have any say.......I will be premptive from now on........my confidence is growing.......I feel like in a confrontation, I could floor someone with a right hand before he is even aware what happened. No bragging but I am quick and accurate...........Nose or chin? I have dreamed of the perfect situation with a left to the solar plexus and a right to the nose or chin in about a half second. I am very passive and do not ever start anything and will avoid things at all cost but you cannot sometimes.........and I refuse to get hit first now. I will either take my beating or put someone on the ground. Just curious how to hit the bag to practice this defence.........again I dont competitively box. I love this forum as everyone is nice and full of advice........it is appreciated when someone experienced helps out. Thx.