Another thought.
If this configuration was possible then it would give the battery connections something much stronger to bolt to. There also wouldn't be any issue with the lug touching the incorrect sheet of copper. The battery lugs could have their own mounting points and not have to share with the ring cap. So the ring cap could then be removed for maintenance etc.without disturbing the battery or motor connections.
I was thinking of using some flat copper bar that i have (19x3.2mm) and getting a fabricator to put it through the rollers and make some neat rings from it. Then weld the joint.
60mm2 of copper should carry a bit of current. If it isn't enough then i could just stack multiple rings on top of each other to get to the required square mm.