So how do we get to the float to check it?
My guess would be that pretty much every bike will be individual when it comes to fuel gauge accuracy.
I would suggest you just get used to it as it is, if you removed the sensor and float from the tank and replaced it it would likely just read differently and not necessarily accurately.
It seems to me its a guide or visual reminder and no more, once you get to know the gauge it will be fine, if fact when it comes to accuracy they are about as much use as an ashtray on a bike.
I think the old peep inside the tank before leaving home is a good guide and after you fill the tank right up set the tripometer on the clock and learn how far the bike will go on a tank full.
The Fazer is the first bike I have owned that even had a fuel gauge, mind you I was off bikes since 1978 to 2012.
Pic below is my gauge with the tank filled almost to the top of the neck of the fill tube on the tank, and it is reading over Full.