I've tried to do a simulation for one and two parallel plates, shown in the pictures below. In the two-capacitor picture there is a wire connecting them that is hard to see.
- The voltage is the same across both the single and the twin pair (9V)
- There is a wire connected the two twin caps but it's hard to see
- Notably the electric field strength between the plates becomes very consistent when the relative permittivity of medium between the plates increased from 1 to 2.
- The field strength between the plates for a single capacitor is twice what it is for two of them. This is the main thing I was interested in.
- The field is well contained between the plates.
- I included a voltage picture for the twin capacitors.
This was in aid of trying to understand about two capacitors in series having a lower overall capacitance than one.