But the question doesn't match up with the subject line of your thread:
How do indies sign exclusivity with companies?
Exclusivity is very different from a one-game deal. First things first. Get a publishing deal with a company and do several games with them and decide if the relationship is good for you, before you bring up exclusivity. But why would you want an exclusive deal anyway? It's usually the publisher who seeks exclusivity with a developer (to keep them from wandering off to someone else).
I think it is obvious not to take unnecessary risk of making F-22 exact copy but what is the line between ripoff and original work?
YOU have to draw YOUR OWN line. How much risk are you willing to take? If you are very risk-averse, then don't use anybody else's IP (draw the line away from it). If you are willing to risk it, then you are moving the line closer. If you don't know what you're risking, then ask your attorney.