Patxipt

Planepounder, our engines are a mix of wet and dry sump. I say this because if you open up the backplate on a 4-stroke after a run, it will have oil inside, normally up to the externall shell of the main bearing. Of course, the oil is always getting renewed by being flushed out at the breather and ingested thru the piston ring blow-by.

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To explain my thought on the post above.
Consider the crankcase sealed, with nowhere for oil to go, except up to the rocker cover and an occasional lose thru the front bearing, and optimum oil level is half full; also, lets focus on the compression and explosion strokes.

During the compression stroke, some oil will pass the ring into the crankcase, as it is compressed inside the crankcase during the explosion stroke, part will go up to the rocker area and the oil level inside the crankcase will remain the same - the small amount of oil that got into the crankcase thru piston ring blow-by as gone into the rocker area, lubricating the moving parts on its way.
Now, what if the rocker area can no longer get more oil? The small amount of oil going thru the ring on the compression stroke will be forced back to the combustion chamber during the explosion stroke since it has no more space to go to. Equilibrium is met!
On our model engines, we never reach an equilibrium due to the breather nipple being situated somewhere on the lower 1/3 of the crankcase or on the camshaft enclosure, letting the oil exit the engine; thus, more oil can pass thru the piston ring gap into the crankcase, being effectively a full lose wet sump. I consider hamaoki's lubrication system indeed a dry sump.