Obviously the bigger the size, bigger the bone part. But it's not necessary true, because breast itself can be wider and flatter or firmer (then you need wide, but smaller size) or the opposite. Or any of that. Cup size doesn't indicate the width. Also chest is completely different number. The cup must sit under boob on the chest perfectly and no space over boobs in the upper half. Now it's live soft material, some hang and some jump up and it also behaves differently. Yeah I can't explain it, long story short - you need an expert to check your boobs and sell you something amazing for <2000 (every half a year) or you find a lucky cheap piece (it's like winning the lotto) or you just strap it in size that doesn't fit properly and give up.