In the context of fighting another human being? Yeah, I believe physical strength of both individuals has a say to the level of courage. If you for some reason had to fight a 200+ pound bodybuilder, or his 140 pound slim friend, and you had a choice, I think naturally you'd choose the 140 pound individual because there is less fear of pain or loss. If you were testing your physical prowess, then you'd probably choose the bodybuilder, because you know he'll provide a better physical challenge. But I don't think your confidence in winning, and in turn your level of courage, would be higher fighting the 200+ guy, challenge or not.