There is an excellent reason to place the "pseudoparity" bit at the gPEAC's MSB: its set/reset rate is 48% so it couldn't encode all numbers, unlike de C or D bit of the binary PEAC.

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However the C/D flag's position is arbitrary. And being grouped/bundled with the parity might not be the best strategy. So how about we put it in the middle ? At bit position 8 for example, it has better chances to trigger an error earlier than if it had to wait for the carry chain to avalanche to the MSB.

It's just a matter of re-wiring a bit. It doesn't change the error detection rate but it should affect its curve's shape, a bit...