I took the index of your words, converted the number to binary, extra 3 zeros, calculated the sha256 digest, took the first part of the hexadecimal to transform it to binary, additional a few zeros for the eight digits of the binary and acquired 00000010011 which translates to 19 in https://bookmarkspiral.com/story19496716/the-basic-principles-of-bip39-passphrase-generator