Originally Posted by soy.lor.n
app drawer -> settings -> security -> improve face matching
if you use face unlock, the "screen lock" setting should be set to "face unlock" and "improve face matching" is the next thing right below that.
ETA: Doing this definitely seems to speed up the face recognition quite a bit. So especially if you're using face unlock largely to have it unlock super fast, you should take the time to do this a few times.
Agreed. I took one of me in a hat, without a hat, in my hoody (hood up), and all kinds of different normal attire.... now it actually surprises me how well it works!