I have just set up an experiment using a tone generator, followed by Dual Pan and then a VU meter such as the Klanghelm VUMT meter.
I have indeed tried all the settings and they all work and respond. It is not so much what the levels are in the centre and extremes
(they do also vary too) but how it changes as you move either of those pan controls in Dual Pan and observe what happens on the VU meter. The various settings produce different results as you sweep the individual pan controls over their range.
Take a dual pan setting like one control fully anti clockwise and the other in the centre position. Observe the position of the needles in both VU meters. Select all the settings in the Dual Pan low settings menu and see for each one a different result in the VU meters. They all work. I think subtle is the name of the game when you are actually panning in a mix situation though. And in the end we still use our ears to set a pan position and level, so matter what the pan law you have chosen at the time you will make those adjustments to satisfy your ear. With any pan law setting that end result is going to be consistent.