With 11 flips you have nice 11 bit number, which you can then convert from binary to decimal representation and then use word on the corresponding line - https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt

Eg you can think about head as 1, tail as 0.

For example:
Flips:            H T H H H T H H T H T
Binary:         1 0 1 1 1 0 1 1 0 1 0
Decimal:       1498 -> Increment by one (because lines are numbered from 1, not from 0) -> 1499
BIP-39 word: robust - https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt#L1499