This has worked for me in past to see what steps voltage is working . As my last card MSI 660ti PE/OC had non readable voltage controller .
Try this , start Heven , hit spacebar (this freezes on that scene ), now with TDP/power% in OSD, check stock voltage (get avg value, it will be pretty stable) .
Now open AB and bump voltage up each step and get reading of power% , if you see even scaling going up then voltage is scaling too.
But if you see no change, then most likely voltage is not scaling up or stopping at a point .
This of course is not going to tell you what voltage, but merely if it has raised and about proportion it raised .
That said, even what you see in GPU-Z is not real voltage, it just a target voltage from driver (not a measured value).