It depends heavily on the dialectric constant of the fuel.
This is unfortunately heavily influenced by alcohol/methanol blended
fuels and other additives which have become popular in automotive
fuels. Unfortunatley, the composition tends to vary dramatically
between fuel brands, seasons and other reasons.
The effect this can have on capacitive fuel probes is dramatic -
rendering them useless.
BWM South Africa some time ago had to retrofit a new series of cars
with normal fuel level senders (they had capacitive probes) after
motorists got stranded due to incorrect fuel level readings.
Rainier