Not sure I agree with the comparison of burst strength under hydraulic load to the consistent flex first in one direction then in the other for every complete turn of the crank. To me this load is more akin to what happens to steel under cold working conditions. Still I have never witnessed breakage in this area so what do I know. The tiny radius may be enough to relieve the stress but if put under a controlled cycling test jig to simulate the alternating forces on the bottom of the BB edges, I wonder how may cycles it would take to fail. Well enough of theory and back to cycling.