Not so much the magic of Android FOTA.. but rather the complexities of every bit of kit inside a phone - all the potentially hundreds of apps users may have installed - humans' flawed sense of memory and accuracy - plus a ton of other variables.. makes it really difficult to comment on any individual SOT vs. FOTA#.
The only viable way is to monitor broadly, if we are seeing any specific issue around battery drain caused - sometimes it can be as easy as Google Play services doing some random thing in the background for a duration of time, causing that particular day's SOT to dip.
