Discussing an unknown circuit using words is almost useless. That is why we have schematic diagrams.
Unless you can show us a schematic diagram of your test circuit, AND WHERE you are measuring the voltage, it doesn't mean much to us.
There are plenty of resources about potentiometers available online.
I spend a few quality milliseconds with Google and found hundreds.
Here are a couple of the better examples I saw after a quick review...
https://www.electricaltechnology.org/2015/01/resistor-types-resistors-fixed-variable-linear-non-linear.html#121_potentiometershttps://en.wikipedia.org/wiki/PotentiometerA potentiometer does NOT control voltage or current. It only controls resisistance.
It COULD control voltage or current depending on how you connect it in a complete circuit.
But when it comes down to Ohm's Law, a potentiometer is just like any other resistor.
If you only connect between the "start" and "end" of the resistance, it is just like a fixed resistor.
Except that you can change the resistance between each end and the wiper.
And a potentiometer is effectively TWO resistors.
One resistor between the "start" and the "wiper",
and the other resistor between the "wiper" the "end" of the pot.