Question - could you be allergic to the materials in the bands??? I am a hard fit - well, let me correct that - when measured they say I'm a 34c - so not true!! I can wear a 36d just fine without issues. Due to weight loss, I do have issues with fit around my sides, but a good bra works just fine.
They are made differently, as all of us women are

some cups are too close together in the front; some too far apart; some cups aren't shaped like me; etc. I dont typically have issues with redness unless I'm irritated by the bra material itself. Even if it fits well, it can bother me and I get the red marks. It took me a while to figure out what materials bother me and what don't, and I just try to pay attention to how I'm feeling on a particular day with a particular bra!! Sweating does make it worse with some bras, so I'm mindful of my activity when in a bra, too.
