The conductors inside the walls feeding from the service panel are already only 12 gauge (or maybe even 14). I would compare to an off-the-shelf cable and request a refund...there's nothing to debate if it's a "same length" cable and laid in exactly the same position so as to avoid the issue of EM field theory discussions creeping in...or its just variances in inner ear pressure. Maybe try a different listener?
I'm having a really hard time with: "Power cable reduced my soundstage"...
My good friend that is in the business and very very knowledgeable calmed that a well made 10ga power cable reduced his soundstage... I'm not saying it will or won't but why would it? I would like to know the science behind this. I did research on here but not satisfied. I had a pair of Logans and they were wonderful and I used stock power cables and the stage was crazy... I have been making cables for years ( musician ) and know the value on quality... what is the magic?