The results of cylindrical F-Layer model [1] are generalized for the case of a flat-layer of an inhomogeneous, magnetized plasma, which seems to be more adequate for describing the Earth's ionospheric F-Layer. Two opposite models are considered: a plasma layer with sharp boundaries and an inhomogeneous plasma layer with smooth plasma density profile. The mechanism of whistlers absorption due to oblique Langmuir waves excitation or their emission outside the F-Layer is discussed. It is shown that this mechanism may be important only in the model of plasma layer with sharp boundaries.