Both the the Slant 6 and Chevy stovebolt cam drives appear to benefit by a pressure squirt directly to the mating surfaces.
I have a feeling (and no more than that) that the rotating gears' centrifugal force tends to spin off any splash oil, and more may decrease surface temperature.
Metering sizes: anything above .030" is supposed to be safer from debris floating in the oil which may block it.