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Cable Capacitance and Barrier/Cable/Sensor Circuit Geometry Evaluation for Intrinsically Safe Circuits

If I’m understanding correctly, most cable manufacturers supply two capacitance values in their cable spec (if you’re lucky).  Those two values are:

Conductor-to-Conductor (C-C)
Conductor-to-Other-Conductors-and-Shield (C-S)

My understanding is that the C-C value is the capacitance between a single conductor in the cable and any other conductor in the cable, usually the highest possible value.  Also, I my understanding is that the C-S value is the capacitance between a single conductor in the cable and all other conductors connected to the shield.  

What I’m struggling to understand is why it is acceptable to reduce what appears to be a fairly complex capacitance “network” down to a single value for use in the “allowable capacitance” calculation for a barrier?

To illustrate my confusion, let me use the case of a 4-conductor shielded cable.  In this hypothetical example, Conductor:1 might be used to power (+) the sensor. Conductor:2 might be the power return conductor (-) from the sensor. Conductor:3 might be the sensor output. Conductor:4 is unused and floating. I would probably go ahead and ground that unused fourth conductor, but for the sake of discussion, let me assume it's floating or used for something else related to the sensor.

In such a scenario, the "capacitance geometry" at first glance appears to be much more complicated than using a single capacitance (Conductor:1-shield). It COULD be that the single-conductor-to-shield (with all other conductors grounded to the shield) is probably the worst possible capacitance and that hypothetically ungrounding one of the other conductors probably reduces the C-S capacitance. So, maybe the C-S value is the limit of how high the capacitance can be, though this is not readily apparent to me.

This may not be correct, but my thought process leads me to say that all of the following capacitances need to be considered and summed up:
1-S
1-2-S
1-3-S
1-4-S
1-2-3-S
1-2-4-S
1-3-4-S
1-3-2-S
1-4-2-S
1-4-3-S
etc, etc. -- Of course, this gets even more complicated because you also have capacitances in series/parallel combinations that I'm not listing.

Instinctively I feel like if I use the C-S capacitance I might be overlooking or simplifying something that I perhaps I shouldn’t. I do realize that capacitances summed in series will reduce the summed capacitance below the value of any single individual capacitance. But it's not clear to me that the entire complex capacitance network would necessarily be reduced down to be a lower capacitance than the C-S capacitance.  

Am I overthinking this or should I just use the C-S value with the understanding that the C-S is probably a very conservative limit?

![Cable Cross-Section](https://electrical.codidact.com/uploads/8magfbxhfysx619wvj0nnumz3and)