There is a document called 485 operating procedure that describes in detail when you can get a waiver for the interview and when you can't.
Here it is (Page 7- 3.24)
Pursuant to 8CFR 245.6 each applicant for adjustment of status shall be interviewed by an immigration officer. This interview may be waived if the Service determines that an interview is unnecessary. The interview waiver criteria are standards set at the national level.
Employment-based:
•The principal applicant is employed by the same petitioner who submitted the approved underlying employment-based visa petition.
•The principal applicant has been interviewed in the course of an
investigation or field examination, and the adjudicating examiner
determines that further interview of the applicant is unnecessary.
•The principal applicant has been approved as an alien of extraordinary ability or alien of exceptional ability and is otherwise eligible for adjustment of status.
•The principal applicant has been approved as an outstanding professor or researcher, or a multinational executive/manager and has a continuing offer of employment from the same petitioner who submit ted the underlying approved petition.
•Adjustment applicants who received national interest waivers based on performing primary medical care to a medically under-served area must demonstrate that they intend to continue according to the terms and conditions of the underlying petition.
So basically if you use AC21 and get an RFE for employment you should be transferred and called for an interview. If you don't get any RFE then you are lucky.