a question!!! Please help.

Say, now I am working in Area A with Salary 60K. And I plan to change job to Area B. But the prevailing wages in Area A and B are far different from each other given the fact that the job duty is exactly same. In this case, which salary rate should be followed to guarantee that my I485 will not be affacted by the job change. I have asked USCIS, they told me that the salary rate should be same or similar to figure in my LC. Is that correct?

Thanks a lot