Here is a photo of the inside of the left cup after being torqued to spec.



You can see where the end of the cartridge crushes the aluminum shoulder in the cup. In my opinion it is not much support for the left side. When I complete this build I will shim around the cartridge to make a snug fit.

I wonder if this is Shimano's solution to the issue of axial alignment. If the the BB is not threaded or faced perfectly the left end of the cartridge may not be exactly centered in the BB shell.