Yes, noted all the perfectly square corners on the pocket as illustrated, I will amend that in my edits to reflect a 1/8" radius when milling as we do on standard lowers.Possibly for manufacturing reasons if it doesn't negatively affect anything. Your front block, the well that holds the pivot pin part of the upper, is impossible to machine as drawn unless you have an EDM. You can't make square interior corners w/ a finite diameter endmill. You can get one edge square, but another will be rounded.
Another spot this is done on commercial lowers: the buffer hole threading. It doesn't need to extend past the buffer retaining pin (its as far as you can screw on the buffer tube.) Its easy to only thread it that far when thread milling. But using a tap the threads will extend all the way across the back of the upper. Doesn't hurt anything. You can see that mega probably tapped it. Noveske thread milled it.
We used a thread mill on the CNC lowers we did and we still milled it all the way...LMAO It does look a bit better stopped just short of the pocket though, imo...
I'm thinking I will stop that cut a bit short of breaking through. As long as the corner of mating plate has no interference, it can be partially milled to clear that corner, but not all the way across the magwell front insert.