I would say, for sure, starting will discharge the battery briefly, but the regulator should bring it back up if it's throwing 14.2 volts. But how long is your daily ride, ten or fifteen minutes? And stop and go traffic where the voltage at idle may be discharging (
12.4 volts for an AGM is quite flat (65%).
I would do a couple things: first, measure voltages 1) key off, 2) after 3 minutes of high beam, 3) during cranking, 4) at idle, and 5) at various rpm (2000-4500)
Second, discharge the battery a few minutes with the lights the "push" the charging with a higher amperage (6-10amps) controlling the voltage manually in the specified range (14.2-14.7, not to exceed 15.0v). Follow this phase with a "float charge for 6-8 hours at 13.5-13.8v (NOT below 13.2v!) Monitor the voltage over a period of hours to days and recharge every time it drops to ~85% (12.65v).
After a few cycles, your AGM should stabilize and hold above 90% for days to weeks.