Noise figure is usually related to low level signals, because the noise of the components si in the same order of magnitude with the signal level.
So any decrease on the noise generated by components is an increase of the C/N ratio.
On power amplifiers, the level of the signal os so high ( Millins times ) that the noise generated by the components is negligible.
Anyway, if you have a very high gain amplifier ( say 70 and more dB ), the noise figure is in the range of 8 to 15 dB.