I took the index on the words, transformed the range to binary, included a few zeros, calculated the sha256 digest, took the main Element of the hexadecimal to transform it to binary, extra 3 zeros to your eight digits of the binary and got 00000010011 which translates to 19 in https://fatallisto.com/story8548133/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool