A band should fit properly around the ribcage, independently from cups. In the bra making community, we always tell people starting fresh to bra sewing to make a band with no cups and get that to fit correctly, first. You can do this process to any pattern you buy, but I highly recommend the Eve Classic band pattern, which is designed to go through this process. (Links at the end of the post) 

In this video, Jennifer demonstrates stitching the band into a fitting band. 





This one of the more well shared articles on fitting bands. It was the first writing I have seen on the subject and I've shared it with dozens of beginners. https://merckwaerdigh.wordpress.com/2014/08/08/step-7-sewing-the-fitting-band/

This page shows how the center front should tack along the center front at the sternum, tight to the body, with no breast tissue behind the wires. Jane shows excellent step by step sewing instructions.

https://janes-foundations.blogspot.com/2019/07/make-tester-band.html?m=1



Patterns for just the band, so you can complete this step in fitting:



Regular wire
https://porcelynne.com/patterns/womens-patterns/eve-classic-bra-band-for-regular-wire/?referrer=CNWR_51041580484060




Vertical wire (better for larger cups)
https://porcelynne.com/patterns/womens-patterns/eve-classic-bra-band-for-vertical-wire/?referrer=CNWR_51041580484060


There's also these variations to the basic patterns listed above: