I had a partial case head separation using a 1.8oz buffer

[DeNinny]

Yes, where the feed cone transitions to the supportive chamber walls is the area I'm thinking of. Rather than a hard angle, it should have a radius. If failure occurred there in battery, there should be evidence of the transitional radius on the upper half of the brass that was supported

I get this and understand your point. Two things:

1) We are not looking at the zoomed in level of the failure. At that scale, there might be more "jankiness" like you are suggesting, which indicates a less clean break over a more rounded surface. From the bird's eye view, the hard angle looks like a sharp edge. Keep zooming in and it will start looking like a radiused "hump".

2) We do not yet know how radiused the OP's barrel was inside. Was the feed cone transition to chamber wall a sharp turn, or was it a smooth curve, or something in between?