I think you've misunderstood my method. We aren't using the Von Neumann extractor here, we're counting the total number of heads and saying "heads" for the resu

I think you've misunderstood my method. We aren't using the Von Neumann extractor here, we're counting the total number of heads and saying "heads" for the result if the count is even, and "tails" of the result is odd. With your D4, that means the HH and TT both count as heads - 62.5% total, which is consistent with everything else.