Question on mutual capacitance change on other neighboring conductors

I am looking for articles or textbooks that can explain the impact of 3rd conductor on mutual capacitance on two conductors.

For example, for many capacitance sensing scheme, the mutual C between sensor and object will change linearly with distance if no other conductors nearby. However, if there is other conductor close to sensor, the mutual C drops much faster with distance.

If any material helps understand this better, I would really appreciate it.

This is a typical Electromagnetic Coupling problem and it's not easy to predict that "approximation effects" by hand calculations. I'm not saying that is "impossible" but it's really hard.that's why we use EM simulators because physical approximation metrics are generally unknown. I mean we cannot estimate an influence how it will act.
There are some rough formulas to estimate coupling structures but they don't give satisfactory results in a complex structures.