Even though the sheath resistances of these gases are very different as a function of the rf current amplitude: The sheath resistance of all three gases align on a single power law curve when plotted as a function of the electron density.
This fit between the sheath resistance and electron density is almost independent of the pressure as well. (At least between 100 and 500 mTorr). Higher pressures produce only slightly larger sheath resistances.
This indicates that an electron density (or charge density) governed phenomenon controls the sheath resistance. (It is also chamber dependent.)