I think we'll be ok. (heating)
I've observed the various theories and practices with underfloor heating/slabs over the years.
The most popular method (used to be) to burry your heating coils, be it elect or water tubing, in a bed of sand below the concrete slab.
the theory was to create more storage, more of a heat bank to help deal with the off peak rate effects.
back then a lot of the installs also had no insulation around the outside or underneath.
the perimeter insulation came first, then people started putting insulation under the sand as well. At the same time, others were choosing to put the heating coils inside of the concrete and they too evolved from no insulation to partial and then full.
There are still to this day 2 separate camps of thought on which way is best, in the sand or in the cement. and within those camps there are still various theories on the insulation part of the install.
So, the way I see it, I just have a little more heat storage with 2 more inches of slab. I am still confident in the system because of the foam insulation that my slab is poured into basically like a mold.
