Inversion layer
You are correct, but remember part of the "land init" is surface temperature. So it is possible to calculate something of relevence. The FMC knows the elevation/height plus isa.
I was passing thru a 1000 ft / sfc inversion layer a few weeks ago, from -10 to sfc of -30. Siberia.
The Auto throttle went ape, and was disconnected rapidly.