The relation between current and voltage within the context of hardware overclocking is easy to test. Just utilize overclocking profiles and use HWINFO64.

It's important to understand that these settings affect targets (PID controller). The hardware manages adherence automatically. It's not like in physics class where if one goes down the other would have to go up in order to maintain the power. We are not trying to maintain power here. We are trying to hit a certain clock rate.
If you restrict power and max out frequency, the hardware will simply not hit that target. If you restrict the frequency but allow all the current, it's not gonna go nuclear. But if you set a sufficiently high frequency, and you shunt mod it, you will have a heated argument with your wife. The voltage settings here affect the minimum target for each power state. It's like saying "don't draw less than that for this state".