I wouldn't worry too much. Electricity is all about "potential". Look at this way...you need to charge your battery and if the battery is at say 12.5-12.8 volts(normal) and the alternator is putting out 12.5 to 12.8 the voltage is the same so there's no "potential" to flow. The alternator has to put out more voltage so the higher voltage will attempt to flow to the lower voltage, IE "potential".
The gauge on the bike is measuring what the alternator is putting out. Remember, the alternator is supporting all your lights, the ECU of the engine, radio, and any other load you might have on the electrical system AND keeping the battery charged. As you ride long distance the battery stays well charged and requires less of a load so the alternator output drops...again..normal. If you start getting massive fluctuations then I'd worry.
I eat, breathe, live, love and ride motorcycles.
4 wheels move the body, 2 wheels move the soul.
2014 Cross Country
Wiseco fueler, Lloyds timing gear +4, Thrush modded mufflers and LLoyds air filter.