I took the index of your words, transformed the range to binary, included 3 zeros, calculated the sha256 digest, took the very first Component of the hexadecimal to transform it to binary, extra 3 zeros for the 8 digits with the binary and obtained 00000010011 which translates to 19 in https://wildbookmarks.com/story18967018/getting-my-bip39-words-to-numbers-to-work