Where can I get more information on capacitive leakage? I would like to learn more about this.
There really isn't a lot to learn without getting into some complex math and engineering.
The simple explanation;
A capacitor is two conductors separated by insulation.
For direct burial, think of the dirt (ground) as a conductor. Yeah it is not a great one, at 60hz, and its moisture content affects its characteristics. Ground could also be a metallic raceway surrounding the conductors.
Next you have the normal circuit conductors.
Then there is the insulation around the conductors.
In any circuit you have at least three capacitors , one between the normal circuit conductors, and one from each circuit conductor to ground.
The longer the length of the circuit the large the capacitor and the more current that will flow through it.
Capacitor current between the circuit and ground is often called leakage current and can cause a GFCI to trip.