A second stage can’t be set to any cracking effort you like. When the exhaust valve sits higher in the water than the inhalation diaphragm, it feels less water pressure, and if the cracking effort is too low, gas bubbles out of the exhaust while new gas flows in: the second stage free-flows.
That pressure difference between the inhalation diaphragm and the exhaust valve changes as the second stage is rotated in the water. It is called the rotational pressure differential, or RPD; some literature calls it the case geometry fault.
This calculator gives the lowest cracking effort that prevents a free-flow in any position. It starts from the distance between the centre of the inhalation diaphragm and the far rim of the exhaust diaphragm, then takes off half the height of the inhalation diaphragm and a little for the stiffness of the exhaust diaphragm, as both work in your favour. Enter your second stage’s cracking effort as well to see whether it is high enough.