OK, so at the risk of being unpopular, would somebody who knows explain to me why TDC on the compression stroke prevents wet sumping; this makes no physical sense. The basic design, which I admire more every time I see something like this, seems to be such as to prevent wet sumping.
The top end is fed through the scavenge pump; drainback, if any, is going to be limited to the volume of oil in the lines and pump, and is going to have to seep past the pump block, etc; crankshaft position isn't going to matter there unless there's a crank position where all four holes in the pump are partly uncovered so drainback has a straight shot through the pump, which I don't believe is possible. If that were the case, then it's going to wet sump a lot and whether or not it's on the compression stroke won't matter. I'm guessing that when drainback does occur it's because oil seeps past the pump block for some reason, this is about the only mechanism. It's still only going to be about a teaspoon of oil or so; there's going to be that much floating around in the crankcase normally.
The bottom end is fed from the other end of the pump, through the quill thingie and crankshaft; the pump is below the level of the crankshaft, as is most of the volume of the oil tank, so there's no real hydraulic head. Oil would have to go uphill past the pump block to get to the crankcase.
So; the "stop at TDC" doesn't make sense; unlike a bike with an elevated oil tank, there's no mechanism for substantial amounts of oil to get to the crankcase. Doing it on the compression stroke makes it even more absurd; the oil system doesn't know where the valves are.
At a guess, when somebody gets the occasional mosquito-fog of smoke, a likely cause is oil past a valve guide; that'll go directly into the combustion chamber and even a tiny bit will smoke like a tire fire. It takes a lot of oil in the crankcase to get some sucked up into the combustion chamber, but not much at all past the valves to make a mess. A little before TDC on the compression stroke means both valves are closed is where the engine's going to stop anyway, but if for some reason there's a good bit of oil pooled in the head that hasn't drained back down the pushrod galley, it wouldn't be a stretch to have some seep past the guides and pool behind the valve. Result; a lot of smoke.
Anybody care to offer an explanation, other than, like deer whistles, it seems to work for them?