I'm looking for confirmation or advice about where a vapor barrier belongs.

I have a concrete slab floor. Underneath the slab is a 5' crawl space, open to the air. I'm in the northeast, so it's cold in winter and hot in summer.

I want to build a room on top. The floor will be 2x6 framing to bring the final floor level even with the rest of the house.
I'll insulate between the 2x6s, probably just batt insulation.
On top of the framing, plywood subfloor, electric heat mat buried in thin set, engineered floor pad and snap together flooring on top.

From what I understand, the vapor barrier should be on the warm side of the floor- so would the vapor barrier on the engineered floor pad be enough?

Or should I use padding without a vapor barrier and install a plastic sheet barrier between the subfloor and framing?

Again, the order of materials top to bottom is:

indoor warm air
engineered flooring
1/8 under flooring pad
thinset with embedded electric heat
3/4" AB plywood
2x6 framing with batt insulation between joists
10" concrete slab
outside air via crawlspace (northeast US climate)

Where is the vapor barrier best installed?

Thanks for any advice or suggestions!