I have comparatively small hands. On an iPhone 6, I usually unlock it with most of my hand near the bottom of the phone to get my thumb in position there. After

I have comparatively small hands. On an iPhone 6, I usually unlock it with most of my hand near the bottom of the phone to get my thumb in position there. After it's unlocked, I shift my hand so that my thumb's coming from the side of the screen, instead of the bottom. In that latter "using the phone" position, my forefinger rests on the upper-middle of the phone, right where the back-side fingerprint readers are located on many (most?) phones. I feel like a reader in that position would make it easier for me to pick up the phone and unlock it without needing to shift my hands back and forth.