In my experience, once you get the split going, it just rolls right down along the grain. I have heard of the run off if you try to split say a third off of a piece though.
Yeah, again not experienced with oasage, but locust, elm, hickory, mulberry, all want to be split in half. half a log, half of that, etc..... right through the bullseye on the end of the log. So taking a good long look, like he's doing, pays off.