I have seen several early lifters which have cracked at the corner between the water table and the standing breach. I believe the change to the radius corner was about the low 14K range.
A tight included angle is a stress riser. The reason is that stresses which develop from a shot need to be distributed so there isn't a concentration at a single point. A radius has an arc which distributes the stresses like a sunburst (or in this case a quarter sunburst) a non-radiused corner only has two directions, 90 degrees to each other, where stress can be distributed. Consequently the stresses are much higher in each of the two directions than if they were distributed around this quarter-arc.
Only just a while back there was a $250 grade lifter that sold at auction, in PA. It was cracked at this intersection. I believe our beloved Stosh (Dave Suponski) also has a cracked lifter.
The second example you linked is likely a grade 2, but if you look at the photos of grade 3 and up lifters on the home page, under grades, you will also see there is a reinforcing bead on the side of the frame, just above the lock plates, at this intersection.
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