It's not what your observed max voltage is, it's what voltage the car spends most of its time at.
The voltage is supposed to vary with the temperature sensed at the alternator (a proxy for the temperature at the battery), so I suggest observing how much of your driving is at what voltage. It always starts high, and then drops down as the engine compartment heats up. If you are putting in many minutes or hours at too low a voltage---It seems that what constitutes "too low" is not an exact science---boost the voltage. Try not to let it go above 14.9-15V for any substantial length of time. The fixed 0.6V boost unit would have worked for my 4Runner, but I didn't know that when I began the voltage adventure, so I figured I'd get the adjustable one. When I first decided to get one, the adjustable units were out of stock. Within a few weeks/months, they became available again. I consider the concept of doing this an experiment, although supposedly thousands of satisfied Aussies use these things on their utes and Land Cruisers.
YMMV-
Results not guaranteed-
Good luck with your "experiment"!