CocoLion - based on my experience in the past 4 years, I believe that adding 4-5" to your underbust measurement in order to calculate your band size is not the best way to get a bra that really adds strong support, particularly for those of us that are quite busty.
I don't want to speak for Maya, but if you have an underbust measurement of 28, I would really recommend trying a 30 or even a 28 band size bra (and go up a cup size or two to make sure you have the same amount of volume in the cup) to see if your support improves.
As far as my own measurements go: currently I'm a bit heavier than usual, and I have a 31" underbust measurement. I wear a 32 band size. If I go up to a 34" band size, I only have decent support for a couple months at most, and then the bra stretches out of shape, starts to ride up, and is uncomfortable.
When I had a 30" underbust measurement, I wore either a 30" or 32" band size, although the 30s were usually more comfortable.
I thought that going down to a band size that is close to my underbust measurement would be too tight, but as long as the bra fits properly, I swear it is a huge improvement.
I buy bras with 3 hook and eye closures to make sure the band is wide and strong - which also eliminates concerns about causing bulging/back fat to spill over the band. I buy bras where the cup size fits me perfectly in the dressing room, but the band is just slightly too snug, because I know within a week/1 or 2 wears the fabric in the band *will* slightly stretch a bit.
It's not uncomfortable, even as I'm sitting or dancing or bending. Because my cup size is large enough to fit me properly, all of my breast tissue is encased in the cup, and the underwire stays in place and doesn't dig in. I don't experience back or shoulder pain, my straps are only minimally utilized for support and the band is doing the majority of the work. Also, my bras last for *much* longer (with good care and gentle washing) than when I bought bras in a larger band size, which means that I am comfortable spending a bit more to buy a higher quality garment.