Some bra fitting questions for interventioners

[OneDayWhenIGrowUp]

How do you know if a band is too small?

Am in the midst of re-self-BI-ing.
My rib cage is 31 inches, so far in some brands 32 bands are ok, but a lot are too loose (can pull 3-4 inches away from me, not flat across the back etc) and in those brands the 30 fits fine. However I've got one where the 32 seems to fit fine, but the 30, I can still get on, just. What are the signs to look for, that a band is too tight? Can a band be too tight?

And second, perhaps silly question, if I'm getting extra under-arm/side boob flab... This means cups are too small?

Getting he perfect bra fit feels like painting the forth bridge... As soon as I've finally got the perfect fit I've put on/lost half a stone and it's all changed again

A band can indeed be 'too' tight. I measure anything between 29.5" and 312 depending on my weight at the time and apart from the Debenhams Gorgeous brand haven't found a 32" that's too tight. A few signs for me that a band is just too small is struggling to get it done up on the loosest hooks, feeling the wires digging in under my boobs and feeling that it's restricting my breathing! I always opt for the smaller band if possible to allow for stretch.

Extra under-arm/side boob flab is usually caused by too small a cup and/or one that's the wrong shape and doesn't extend round your body enough to encompass all the breast tissue properly.