I have the sizing figured out. I wear 36c and bought three sizes: 38, 40 and 42 in several of the styles listed.

My favorite nylon Bali, 36C bra is 30 inches across the band unstretched.

This bra in size 38 is only 27 inches across the band unstretched.  Size 40 is 29 inches; and Size 42 is 31 inches.

38 was so tight it left red marks.

Not surprising both 40 and 42 worked for me because my regular size was in between. In all honesty, size 40 was best and 42 moves around a bit, but since I'm going for comfort and just something to tame the headlights, 42 also works.  Some ladies may like it tight and squishy, in such case, order up one size.  I found 2 sizes up perfect.  3 sizes up for easy loose comfort still offering light support and taming of headlights.