I didn't start this thread to bash on he placement, it is what it is, it works well. On a Samsung device if it's not on the home button on the front it's different and you need to retrain your brain now that it's now on the back. Maybe it's a male thing but I keep forgetting which side it's on of the camera, if I flip it over it's on the right, with it facing me it's on the left, I know I know I'm easily confused.
Last night laying in bed while the wife watched TV I played with the iris sensor with no glasses on, retrained the iris and in the dark with my eyes half asleep that thing work every time, sometimes so fast I didn't think it even locked to begin with. So now I know it's my glasses and it's time to get some new ones and see if it helps. I'm already thinking of "what frames would work better for the iris sensor".