Greg,
as you can see I wrote "in principle". In practice some diluition with kerosene may happen also with four strokes, since the liner, particularly at the end of aspiration phase, shows ample surfaces at temperatures lower than the final distillation temperature of kerosene, and some kerosene goes also in the crankase mixed with oil, lowering its viscosity.
Maybe you know this, but a problem arising with commercial oil additives comes from the need of using some kerosene inside for keeping ingredients in solution. This may cause damages to the liner due to the tendency of not evaporating, wetting the surfaces and lowering the viscosity of the oil.
I have not your good memory, but were not you complaining of a broken ball bearing owing not to have used a shielded one?
Ugo