I took the index of your words, transformed the range to binary, included a few zeros, calculated the sha256 digest, took the main part of the hexadecimal to convert it to binary, extra 3 zeros to your eight digits on the binary and got 00000010011 which translates to 19 in https://brightbookmarks.com/story19102382/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39