I don't see a problem with your charging system.
At idle, the bikes stator (and your AC test confirm it's working fine) is not putting out a lot of power. Also, the fan and lights use a lot of power. So seeing 12.7 at idle with the fan on would not worry me. I am guessing you just started the bike and let it idle to warm up. In this case, it's had very little time to bring up the battery to a fuel charge. If you road the bike around for 10 minutes, then you would see a higher voltage and the fan turning on would make less of an impact.
And as long as the charging system gets into the mid 13V at cruising speed, then I would also not worry. 14V is nice, but can overcharge a battery if it stays at that voltage for too long. But AGM batteries like a higher voltage.
The best way to charge any led acid battery is to bring it up to 14.2V at the recommended charge rate of. Then float them at 13.5V. So ones the regulator sees 14 or so volts, it may kick down into float mode and drop the voltage down.
The rectifier/regulator on a motorcycle has a lot to do and can control very little. It can't control the amount of power coming from the stator like in a car alternator. At idle, the amount of power coming from the stator may be just over the amount needed to run the bike, leaving little for battery charging. But at 5,000 RPM, the stator is making way too much power and the regulator has to burn it up as heat.
As fast as the 9x0 revs, the regulator can have a tough time keeping up. But it does not really have to as batteries are very forgiving of voltage/amps spikes.
I have a volt meter on my 950 and the voltage has always been all over the place, but it's in the 13V range when cruising and that is all that really matters. I got 6 years out of the stock battery. But I do keep it on a trickle charger when I leave it parked for more then a week.