Installing new hearth over chipboard floating floor

[Buffon]

We recently had to have all the chipboard floating floors replaced downstairs due to flood damage. When removing the damaged floors, the builders also had to remove our fireplace and marble hearth. Now that the floors are all back in, I'm ready to install a completely new fireplace.

I first need to install the hearth, but I'm slightly unsure about the correct approach. I obviously can't bed the new hearth directly on to the chipboard floor, so I've cut out and removed an area of chipboard within the area to be covered by the hearth. This exposes the DPM which in turn lies on top of the Celotex insulation.

Can anyone confirm that the correct way to proceed would be to lift the exposed DPM, cut out and remove the Celotex insulation, drop the DPM down onto the concrete beam-and-block subfloor, and then fill in with concrete up to the level of the top of the insulation?

If this is correct I can then place my dabs of adhesive/cement onto the concrete when dry, and bed the new hearth down onto the dabs, leaving a small gap underneath the edges of the hearth to allow the chipboard flooring to continue to float.

Does this all sound sensible, please?

Many thanks