The bra band will give the majority of support, so you want to make sure it’s a correct fit. When you get a new bra, you’ll want to make sure you are using the first clasp.
In between your two separate underwire cups is what is called a “gore”. The center gore should be tact against your sternum.
If your breast tissue overflows or if there's a gap, it’s a sign that you either need to change bra style or get a different cup size. A proper fitting bra will provide a smooth appearance.
This is a technique you will do after putting on your bra to make sure the breast tissue is pulled from the sides into the center of your body.
The underwire should not dig into your underarm or rest on you breast tissue. If it does, it’s most likely a sign that you are in the wrong size or style of bra.