Wow!.. That seems counter to everything I know about engines.... The piston creates pressure in crankcase as it travel downward .. if theres no airspace , to absorb it, the pressure plus the expansion of oil that is hot, should force oil thru the rings and into combustion, fouling plugs . ...and with higher level of oil, the crankshaft is submerged and begins whipping the oil into a foamy mess.. foam does not lubricate .. thus bearing damage occurs .. plus the pressure causes oil leaks to start. maybe you are just at the critical level ? Dont know, but I fill mine to high side of mark with dipstick not screwed in ... never had a clutch fail in a dozen ATV, UTV over 40 years ... and NEVER use full synthetic oil for cars in them... only wet clutch oil