Don't move now. I guess u were made SA ahead of the typical four year time frame in your firm. You should move when you are 3 year 10 months (join the Tier 1 firm then) and ask for batch parity. That's your optimal case scenario.
No chance they are going to give you SA when your batch people who are home grown are stil A3.
In my limited experience, it is possible that they may hire you as an A3 and promote you post probation or in the next cycle basis evaluation. It will depend on various other factors but it is a sad reality that they will try to discount some of your experience as it was not in a T1. Negotiation is key here. if you have good grasp on the subject and are making the move in a same practice area please negotiate hard for SA or atleast SA promotion post probation.
I'm working as a Senior Associate in a mid-sized law firm in Delhi and planning to switch to a Tier 1 or Tier 2 firm. I have 3.5 years of PQE. Should I expect a demotion to an Associate level?
No chance they are going to give you SA when your batch people who are home grown are stil A3.