Did you actually understand reply#5?
You can’t put more than 0.6V into an analogue pin than the supply voltage of the Arduino’s Vcc which in itself has a maximum voltage of 5.6V.
So putting anything over 5V into an analogue pin will screw up your Arduino, and anything over 5V, the Vref voltage by default will not give increasing readings.
Vcc is NOT the voltage you put into the power jack, that is regulated down to 5V to provide the Vcc for the Arduino’s chip.