Shower drain trim

[Scott Gallison]

I am in the process of redoing my spare bath. Got shower stall (no tub) all set to go, and new drain trim is supposed to be here today. The old drain trim was a simple 3" chrome circle that screwed to the drain pipe ( 2-7/8" screw centers). The new one has a similar cover, but comes with a 4" outer square trim piece. The shower floor is existing sloped concrete. Do I layout thinset, and set the trim piece IN the thinset, or do I set the trim piece in something like silicone, and then tile up to the edge of it? Thanks