Mahle/Clevite did some testing on the oil grooves and found the half groove oiled better than the full groove. It's in the performance bearing catalog.

"While a slightly shorter groove of 140 degrees
provides a marginal gain, most of the benefit
is to the upper shell, which doesn’t need
improvement. On the other hand, extending
the groove into the lower half, even as little as
20 degrees at each parting line (220 degrees
in total), takes away from upper bearing
performance without providing any benefit to
the lower half. It’s also interesting to note that as
groove length increases so do horsepower loss
and peak oil film pressure which is transmitted
directly to the bearing."