^^^ this
Adam recalls how these were prone to cracking.
Any slots that go to the edge, and at right angles to the edge, are prone to cracking.
It's the same principle where...
* a glass cutter needs to go right to the edge for glass to crack - if it doesn't it's hard to snap
* a tablet that is scored across the middle to enable a 1/2 dose needs the scoring to go to the edge to facilitate cracking
So you wouldn't want to have your rotor slots anywhere near the edge; or worse still, perpendicular to the edge.