What is the difference between '잖아' and '지 않아' in a question?

The expressions '잖아' and '지 않아' convey different meanings when used in declarative sentences in Korean. For example, '저 옷은 비싸잖아' implies 'Aren't you aware that the dress is expensive?' while '저 옷은 비싸지 않아' simply indicates 'The dress is not expensive.' So, what about in questions? For instance, '저 옷은 비싸잖아?' and '저 옷은 비싸지 않아?' can both be interpreted as 'Isn't that dress expensive?' However, there may be subtle differences in nuance between the two expressions. '잖아?' feels like a confirmation of a fact that the other person already knows, while '지 않아?' is closer to a more neutral and general confirmation question. Understanding and using these differences is important. I'm curious about the opinions of Korean language experts. How do you distinguish between these two expressions?