Capacitive touch sense problem with battery powered laptop
For a touch sensor to work it must increase the capacitance significantly between signal and return.
For a localized pair this means the existing capacitance must be low.  If the terminals are coplanar , you might be adding at least 50pf to 5pF with no ground plane under it, then when bridging the surface  air gap, you don’t even have touch both contacts when coated with soldermask.  If you have two spiral terminals closely spaced, you can touch anywhere inside the spiral.
For an isolated terminal, it relies on your return path to ground return.
Using a higher kHz frequency naturally lowers the impedance of all localized and finger capacitance equally, but makes it easier to shunt stray E-field noise with a smaller load resistor.