I find it strange that you are unable to increase the distance
aswin, actually I'm curious why you're asking this, do you suppose me to be not sure about my own requirements?
I actually don't find it strange, it is as it is because I have to place the sensors (actually 3 of them) halfway inside and outside the middle of the claw of my chess robot to center the pieces exactly before grabbing them.
The accuracy of measuring the center of the pieces must be less than 4mm. That requires a detection angle of about 10° or less at a distance of 1cm, but for 6cm min distance the detection angle has to be less than 2°!!
So do if you don't know a sensor which has a min range of 1cm with a detection angle of less than 10°, could you probably suggest a sensor which has a min detection range of 6cm with a detection angle of less than 2° instead?