General :: Nexus 4 With Jelly Bean 4.2.2 - Making Face Unlock More Reliable?

I'm using the Nexus 4, with Jelly Bean 4.2.2 (stock ROM, rooted). It works great, and I've got face unlock working... mostly.I'm trying to train it, by going into Settings->Security->Improve Face Matching periodically, but it still only recognizes my face about half the time.

Often, the lighting is bad - maybe it's too dark, or I'm backlit so my face is turned into a silhouette - there's not much to be done there, but often, there are borderline situations, where the camera shows what I think is a recognizable picture of myself on the screen, but the phone says "Sorry, I don't recognize you."

Does retraining the phone often enough eventually get the facial recognition system to work better? Or is it always going to fail here and there if the lighting's off?Or are there any hidden tips based on whatever algorithms the face-unlocker uses, that would improve my results?