An installed voltmeter to view while riding is a great help too.
I have adjusted my bikes (CB750) stock regulators numerous times to get proper charging and avoid too high voltage after 1 hour ride or more.
That way found how to adjust the regulator.
Core gap 0.8-0.85mm.
Not less nor more. I have tried it on 3 different regulators.
Almost no charging to overcharging 15-16V and more.
Both bikes with Dyna-S. Dyna 5 ohm coils and new Honda stock.
LED H4 headlight taking 30W. LED rear lamp, around 5W despite braking.
Stock blinkers 21W each, visible on voltmeter when used.
Wrong setting of core gap will also make a big difference if the headlight is on or off.
The other "relay" contact ca 0.35mm. Manual says 0.30-0.40mm. 0.30 feeler gauge in by ease, 0.40 not.
All electrical connections must be clean with good contact. From alternator- regulator- rectifier- battery.
A pressure washer can if aimed wrong cause corroded connections rather quick.
Good ground. I have installed extra ground wire between rectifier and battery. A thick wire, had to use yellow crimp ear.
The Bosch regulator is interesting. I need to have a look searching......
Here idling with headlight on. Will reach over 13V before 3000rpm.
Max 14.5V, often around 14.3V. For me OK when 14V or more most of the time.
I have tried setting to get 14.5V most of the time on long rides. The bad thing is occasional 15V area.