Think of it like Paxos. As long as a majority of unique data points agree, allow access. That way if your back is out which results in your posture being unrecognized, the other factors can still form a quorum and grant you access. There could be 20 such factors weighted by "difficulty to forge", so that a fingerprint counts 15x as much as posture for example. Then if you successfully authenticate with, say, 80% on all data points then the system can allow you to train a new factor.
