occlusion culling cell size...

Hi guys

i am trying to use occlusion culling in my project for best performance and i know how to use it but as stated in unity reference for occlusion culling as i reduse the cell size it going to effect my games performance

so now the qustion is i am not getting how to reduce the size of the cells or where i can find that thier is a option in bake tab (View cell size) but by changing them also dose not effect on the cell size

so can some one help me with this that how to do it

Thanks

AR