ugo, what your saying is true , BUT , its not all the story re lubrication.
A lubricants ability to do its job is also effected by its molecular size-this doesnt change with dilution, and its molecular polarity which effects its ability to adhere to metal surfaces- this is were vegitable oils in particular reign supreme over other oil types- vegi oil molecules tend to stand vetical from metal surfaces whilst being electrostaticaly adhered wereas other oils tend to just lay about as a jumbled mass and are more easily wiped off the surface.
this tends to make vegi oils -castor/modded olive oil , act independent of dilution factors moreso than mineral/synthetic oils.
Stewart