Hello Madhu,
for gear tooth counting, there are two rules of thumb to achieve best performance:
- To detect the conductive target reliably, the physical size of the inductor should not exceed the size of the target (ie the gear tooth).
- The distance from coil to teeth should be less than 50% of the coil diameter.
Therefore, a physically small inductor close to the gear teeth will provide better performance than a large inductor at far distance.