Being regulated, the Fox should be at a lower pressure. This means that the pressure curve behind the ball is different. The pressure on the Fox should be relatively lower and longer, where the cat has a high pressure punch to it. With the empire kit, try a longer tip and maybe a lower velocity on the cat, so that it is not blowing a lot of gas.
Hooking shots often come out of higher velocity with short barrels, which also plays into the regulator on the Fox (less spikes). CO2 gas on a cold day is no help for the cat. If you have some volume in the front grip of the cat and tune it down for a long barrel, it should stop hooking.
Different valves/pressures like different barrel arrangements.