Different H1B Transfer and H4 Extn USCIS service centers

[user2018]

Hi,

I recently moved to a new job and my H1B transfer was filed with California Service Center. My spouse's H4 extension was filed last week by new employer. Today I received a reply from Vermont Service Center for receipt. I would like to know how is the service center decided? The reason I ask is because H4 Extension processing time in California is 1-3.5 months whereas in Vermont it is 10.5-13.5 months? Can petitioner request for a specific service center? Thanks.