The ubiquitous positive streamer

Liquid insulation occupies a key position in the range of electrical insulating materials. We can conceive of a volume of empty space to which matter is added, molecule by molecule, until the vacuum is transformed, in stages through low pressure gas, high pressure gas, liquid of low viscosity, liquid of high viscosity, to an amorphous solid. First assumptions might be that as the phase changes then so does the breakdown strength and breakdown mechanism. Yet the indications are that there is no sudden change in the breakdown strength as we go from gas phase to liquid phase at constant density. Why therefore should we suppose a change in mechanism?.