My back has a natural V shape to it and I’ve got pretty developped lats. Add to that the fact that I’m not too tall and have a shorter torso, so that the V is more dramatic than in a taller person.
To illustrate that, the infamous Victoria Secret fitting style would put me in a 40 band, as my overbust is not 4, not 5, not 6, but a whole 8 inches larger than my underbust. With an underbust of 32 inches. The +4 method would put me in a 36 band, the +0 in a 32. Yet, I find that a 34 is usually the best fit. My guess is that it is due to my back shape.
While some 32 work great (Hello, Oriental Bloom!), with most, I find that the lowest hook and eye closes easily, but the top one is pulled to tight.
This is what ends up happening:
First two pics are Panache Harmony, third one is Bravissimo Alana.
As you can see from the third pic, the eye of my bra was pulled so tight that it actually fell off! Ideally, I would need a 32 on bottom and a 34 on top! For now, I just make sure to try bras in both sizes and check which one fits best.
I wonder if any manufacturer takes into account the fact that the back is wider than the underbust for many women and if there are some bras more suited to that back shape than others.