I have radiant baseboard heat in my home (water/boiler system). I have removed my old floor down to the slab (no basement) I am installing new pex tubing on top of the old slab for a new in floor radiant system. My question is: My slab has about a 3rd of a 400sq. ft. area that is 1 to 1.5" lower than the rest of the slab. Do I need to level the slab before installing the new system (so that the finished system has all the new pex tube at the same depth into the newly pored concrete.) Or, if I don't level will the heat simply radiate up and not relay make much of a difference?