Why does increasing resistance make a capacitive sensor more sensitive?

Question

From the Capacitive Sensor Page on the Arduino website, it states the following:

The capacitiveSensor method toggles a microcontroller send pin to a new state and then waits for the receive pin to change to the same state as the send pin. A variable is incremented inside a while loop to time the receive pin's state change. The method then reports the variable's value, which is in arbitrary units.

AND

Use a 1 megohm resistor (or less maybe) for absolute touch to activate. With a 10 megohm resistor the sensor will start to respond 4-6 inches away. With a 40 megohm resistor the sensor will start to respond 12-24 inches away (dependent on the foil size)...

However, as mentioned above, what I'm measuring is the time taken to change state, and I understand that more resistance = more time taken = higher value, how exactly does increasing the resistance make the sensor more sensitive, allowing it to respond without even touching it (i.e., inches away)?

Am I not simply increasing the time taken to change state by increasing resistance? How would that make it more sensitive?!?

Answer 1

A capacitor is created from two conductors with a dielectric between them. The capacitance of the capacitor is determined by the surface area of the conductors and the distance between them. The larger the conductive surface, the higher the capacitance. The further apart the conductors, the smaller the capacitance. Using a higher resistance means that you can use a smaller capacitance, i.e. be further away from the sensor, to get the same results.