Did a quick mockup test with a Tesla Extra coil to see how increased surface and bulk capacitance affects the result.
Surprisingly, despite the coil being a huge dielectric resonator, covering the entire thing in LDPE tape had no measurable impact on the resonant frequency, nor the Q (resonance) factor. Still incredibly sensitive to just moving your body or hand a few feet away.
I then performed a ‘bulk’ capacitance test by covering the coil with HDPE plastic scraps i had laying around. This did lower the frequency, and surprisingly actually increased the Q factor.
For Tesla coils, the higher Q the more resonant it will be, and the better it will perform.
The test throws out some of our assumptions, as it means that as long as a low-loss plastic is used, the mass or surface area of contact does not seem to matter at all.
It al means we might be able to mass-produce these coils using a low-loss pipe. NOT PVC though, as it is horrific at RF frequencies.