tylerni7 t1_jba5rgd wrote

The distance will affect the field strength, which will fall off as the distance cubed.

However, this is NOT the same as efficiency: if the stove ran with no pan coupled to it, the power usage would be low (only resistive losses and some negligible energy from the field permeating the air).

So while things will get slower further away, the stove will also use less energy. Trying to estimate the actual effect is tough and depends a lot on practical things (like the specifications of the coil and its drivers and the magnetic permeability of the stovetop and surroundings), but it's probably fair to round it to zero in practice.