I did an experiment once and removed the sensor from the POS cable that controls that regulation for about a week. It worked. But on longer road trips it seemed to create a slight burnt electrical smell from under the hood from the constant high charging and it freaked me out so I put it back on and left it like it was.Yeah, but the lowest it's ever gone has been 12.5 previously.
It shouldn't ever regulate lower than that. And in my opinion, since it's literally just for fuel savings, I'd be happy if I could program it to push 13.5 all the time.