K7102 Metal Detector

i am currently working on k7102, i want to increase its range by atleast 4 cm, so that the total range becomes approximately 12 cm. I have tried changing the coils, but in vain.
Can you please tell me what should i change in the circuit so that the range is increased.

Sorry, we never test any range exchange for this kit.

can you provide any information on how this circuit works?

Sorry, no circuit descriptions.

[color=#000000]Is that metal detector a [/color][color=#000000]gold detector[/color]?

Sorry, no. It has been designed mainly to detect metal in walls, to avoid damage when drilling hoes.