I vaguely recall the torment of having to accommodate changes from 3 dimensional to 2 dimensional heat tranfer across gaps that approached micron scale when I was doing thermal work a long time ago, so you can get weird effects even at engineering scales.You'd be surprised. Certain high end automotive components actually have to take quantum effects into account due to their tolerances*, which aren't nanometer scale
*Generally the Casimir Effect causing resistance/pressure to be different than it should be without accounting for quantum effects
And once down to a few 10s of nm or even smaller, everday expectations can be wildly out even before allowing for true quantum effects to cut in.