Just popped this up in search, just out of interest this is because copper is a BETTER conductor as you say, but heat will transmit more through it making it read higher than average.
To simplify imagine when you touch a car on a very hot day - if you touch the plastic bumper it'll be warm, if you touch the metal bonnet you may get burned. Naturally it's not literally that hot outside, otherwise you'd be frazzling, however the metal conducts and accepts heat far better than rubber, plastic, our bodies etc.
this sme conductivity is why it's used for electric cables.
So wrapping your sensor in copper tubing would mean it'd sense much higher than reality in the rest of the floor....
hope this helps clarify!