Another note is that the crew of your ship seems to have something to do with it. In my experience if you take out an enemy in a ship with a much smaller crew, it has a greater effect on your CR than taking out the same enemy with a larger crew. It seems to give you more credit. Since I frequently take out Voinian ships while flying a fighter, this is something I've seen many times. I've jumped from Harmless to Noteworthy with one kill.
So if you want to improve your CR, consider switching to a ship with a smaller crew. Crescent ships are good for this. I'm guessing that you're in a Voinian ship at the moment, and that might make it take longer to improve your CR.
If I remember correctly, you only need to be Dangerous to join the Zachit. But if you check at their Outpost, it says in the description what the minimum level for a Zacha is. They also need to like you quite a bit, so you should kill lots of renegades in the area. I think your legal status has to be Good Egg.
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Paradigm, Captain of Industry
And when you stare persistently into an abyss, the abyss also stares into you. - Nietzsche