Well as shown in the picture to bowl a leg break the ring or turning finger should be in contact with the seam, the middle and index fingers should be rested on the seam with a comfortable distance, finally the thumb can be in contact or can be with out contact with the seam since it plays a minor role in spinning the ball, in this type of basic leg break bowling.
The three fingers index, middle and ring are the key in gripping or spinning the ball from right to left. And among these three fingers again the ring finger plays the major role since this is the turning finger which is used to spin the ball from right to left along with the seam in the direction of slip region. That’s why we call this ring finger as spinning or turning finger.
The gap between the middle and index fingers shouldn’t be too far or too close but has to be a comfortable distance which finally depends on individual.
At the end of the day the whole grip has to be a comfortable grip but shouldn’t be too tight or too loose grip.
Well to get a rhythm of comfortable grip you got to practice or got to be habituated in spinning the ball from right to left along with the seam right up in the air.
Before every ball you try to bowl, do this exercise repeatedly, surely you will be getting a nice rhythmic comfortable grip, which allows you to turn the ball from right to left along with the seam in the direction of slip region at the time of releasing point by spinning the ball in vertically slant up direction in parabolic style.