To abbreviate my voltage recommendations, I usually post a maximum permitted voltage value. In the case of charging with a generator, a 14.7 absorption charge limit rather than 14.4 volts would reduce charge time enough to matter. When a "smart" charger develops enough power to become a constant voltage charging source, the only way for it to determine the state of charge of the battery is to measure, define, then control the charging amperes by deflecting to float mode.
14.4 volts for an AGM battery is fine. It is just a lot slower for the last 15% of ampere hours of charge.