I feel similarly, and I can barely hear the differences when I feel like I should be able to. So I’m looking for tips myself.

not golden or not diamond, but probably problem is a your place, studio whatever it is, try compare headphones and speakers results in the game, try move speakers around your room. still cant hear any difference? Take your time to train your ears

Personally, I like to reference what I'm hearing with what .2 or .8 may sound like in my mind. That or think of .1 or .9 (Granted this is more intuitive I think). I agree with you that it's difficult to tell the difference, but I know that with more practice, you do eventually come to tell the subtle difference. :)