FDC1004EVM: Can it be used from a distance，12mm，8mm.

FDC1004EVM,With customer plate test（the plates are tiny, about the size of a fingernail）, the chip output fluctuates greatly in the desired detection distance, and the useful signals are basically drowned out，when in 12mm，8mm，what could be the reason，Can it be used from a distance.thanks。