The holes weren't symmetrical, nor did they really help with the control. If that was the case, there wasn't a need for there to be so many of them. It was strange for that particular portion of the weapon to have such a meticulous design; it had to be custom-made. Why wasn't the thumb indent more prominent?
In that instance, Wang Zhong discovered a detail of the weapon that he was missing out. There was a depression located on its axis which made it a very suitable position for one's thumbs.
With a bit of soul power, his thumb pressed down and adhered to the small recess. The crosswheel started to rotate, but this obviously wasn't how it was supposed to be used since his fingers should be placed inside the holes.
Changing up the method a bit, if the forefinger is placed there, while the thumb spins it…
Middle finger… pinky… when no finger was placed at the centre, the rotatory feeling was different.