I think it depends on the hawk, too. Some smaller hawk species might not go after large chickens unless they are desperate, like needing to feed their chicks or during a shortage. But large hawks (and owls and eagles, for that matter) can carry off even larger chickens. Smaller hawks can kill a large chicken, but will eat it at the kill site if they can't carry it off.
It has really helped me deal with my hawk issue to know which hawk breeds I am dealing with. I don't have Red Tailed hawks that hunt in my neighborhood; they stick to the open areas like the rice paddies, the golf course, and the big ranches in my area. Plus, I have a lot of trees in my fenced yard, so my chickens are able to hide from the soaring Red Tailed hawks. However, those same trees are perfect for providing cover for Cooper's hawks, who prefer to stalk their prey first. A Cooper's hawk can't carry off any of my big girls, especially since it's a smaller male that's been hanging around, and they are 2 and 3 times his weight. He is less likely to strike when I'm supervising because he wouldn't be able to stick around and eat if he managed to kill one of my big girls.
My bantams, however.... I hover over them like a mama hen when they are out foraging. If I don't feel like hovering, I will just let my big girls out and keep the bantams penned. That way I can supervise, but relax a bit. And the bantams don't mind being confined nearly as much as my big girls.
I hope that makes sense. Sorry it's such a long winded explanation...