Alan,
The big end of the connecting rod projects out a little further than the swing of the butt end of the counterweight. So they would ‘splash’ first. In theory the later squared-off counterweights would create more windage and so throw more oil mist about. But indicators that they were coming to grips with oil control- such as better oil control rings, elimination of the anti-fouling pockets for the sparkplugs, and discarding the total loss oiling system- all came long after the change to squared counterweights. Since the squared counterweights came along about the time of the switch from 68 to 82mm stroke cranks, I suspect it had more to do with needing more mass to increase the balance factor. Possibly even increase the counter-torque for the rocking couple, but that might have just been an side benefit.
Determining the balance factor at that time was likely a matter of trial and error. So there will probably be examples of early square, and late chamfered counterweights to muddy the waters. I know recently a fellow chamfered a set of mid-thirties counterweights; perhaps thinking it was a racing modification. It would indeed drop the inertia of the rotating mass, at the detriment of upsetting the balance factor.
Speaking of splash lube, I do not think many realize the importance of the dividing rib cast in the bottom of the DT type crankcases. Often you see these broken or even purposely chiseled out. The intention was to create two separate pools of oil, with a small hole connecting the two. The small fins or dippers on center web straddle this divider. When the dipper strikes the pool of oil, it knocks most of it out off the way, with a little hopefully being driven into the sides of the big end bearing where it might do some supplementary good. Then along comes the other throw, and smacks into the pool of oil again. Were it all one common pool, the level would only have half a crank revolution to recover. With two separate pools, each side gets one full revolution of the crank to recover, or twice as long. Not very long at 5500rpm, but every little bit helps. So goes the theory. In practice there were other engines they made that did not, or could not (ones with sumps), have this divider.
-Doug