The shape is to ensure it can back out easily. The body is smaller than the drilling radius and all the edges are angled so it won't get stuck. You basically can't get this thing stuck. Nowadays there's not that much actual heavy armor left on it, it's mostly just a frame to recess everything else into.

oh, that explains it's shape

It's meant to be carried on the spine of my Pioneer-class Mothership and the Sturgeon-class. This is an ancient design, the first version of which was made in 2014 (it's in my workshop). It's been continually improved and is well-optimized. One thing of note: it's an entirely heavy armor hull, and everything is recessed. It can take bumps. This was also to give it the inertia to resist drill torque (the insane number of lateral thrusters is also for this).

it looks like it could slot in seamlessly into a larger ship that could carry it to it's destination