When I tested....Most rock zero response. Apparently too many inputs and not enough attention to coherent phase in the recording process.
Some solo instrumental, it makes a difference. Live albums? That seems to work sometimes, too.
I took an online test using earbuds, which I know not to be 'best case' and scored 50% correct. Maybe I'm not sensitive to this phenom.
It may not help that I am a 'set and forget' type. The remote for the amp, with the phase control is over on a shelf......somewhere........It may not even have batteries installed, since it it so infrequently used.
As far as the original post:: The speakers can either be identical or 'mirror image'. So, looking at the back of the speakers, the posts can be A/B//B/A or A/B//A/B. That's why I recommended starting with getting them in phase. The rest? Have fun! Swap the leads around to hearts content.