I've had a much different experience with CX, with them ranging better than any breed I've ever had simply because they are very hungry. Here's a vid of the last large batch of CX...ranging and flying. This batch even roosted as high as 3 ft off the ground. They were fed once a day, fermented layer and whole grains, after they had ranged all day long. Pardon the very poor video skills...my very first such things and done on a still camera.
My first batch were raised by a broody hen and lived with the layer flock. They too ranged very well, all finished at good weights after only being fed once per day after foraging all day. Didn't lose any of either batch due to health issues or predators, though they ranged far and wide.
I admit I did not care for the bird. But I also admit much of this was due to my lack of knowledge and that they did not meet expectations. They get too big to be willing to move, unless they are starving. If used to ranging for their food all day, I can see how constant excersise would make them hardier, but if not ranged all day they become too large to move without pain.