Well, the last time I was involved with u/floor heating, we had a real oak floor glued down to a sand & cement screed. Embedded within the screed was the heating pipework. Under all of this was the insulation. A normal way of going about it.
I would stick my neck out and say that your problem is unlikely to be anything to do with that.
U/floor heating runs at quite a low temperature (compared to rads). There should be no high temp. hot spots.
Do you have "zoning" controls on the wall (rather like roomstats) that give you control for different areas? I would suggest the problem lies with the control gear rather than the pipework.
Zone control is quite a specialised area. It really needs someone experienced to take a look at it.