FDC2214: [FDC2214, LDC1614] Finding the optimal LC tank(inductance and capacitance) to increase sensing distance.

Hello,

I am currently using FDC2214 and LDC1614 on separate PDB boards to detect proximity distance.

For FDC2214, two large semicircular electrodes with 60mm diameter are used as the sensor.

For LDC1614, a hollow coil with 60mm diameter is used as the sensor.

I goal is to detect the human body from more than 20cm (25cm is ideal).

However, my sensor can detect no more than 10cm.

Many answers on similar questions say the sensor size is not big enough.

But I don't think it is solely about the size because depending on what inductance and capacitance (LC tank values) I add alongside the senor, the sensing distance change dramatically.

Sometimes it can detect up to 10cm, but sometimes it can only detect about 3cm.

Hence, I think finding the optimal LC tank values is important.

However, the specific correlation between the LC tank values and the performance of LDC1614 and FDC2214 is not described in the datasheet.

So my question is, on what basis should I select the optimal LC tank values?

Is there any theoretical basis, or specified rules that I can follow?

Thank you.