It's based on tank size. I expect you have a 20 pound tank. As that is all i have seen on hrr's. But a 20 pound tank is what you see sitting at all the tank.exchange places, and is what a large gas grill uses, it's probably 16 inches tall. A 30 pound tank is probable a bit over 24 inches tall.
The 2 covers you linked are for dual tanks. My X17C has a single 30# tank; not sure what your X17Z has. I have been unable to find a hard cover for a single tank; only soft vinyl ones.