Noise analysis for FET transistors

I am trying to do a noise analysis of a GaAsFET amplifier.  According to the literature, the dominant noise source at high frequency (1-50MHz) should be thermal noise from the channel resistance.  We should only see shot noise in the gate-source PN junction, and it should be extremely low when reverse-biased.  However, noise analysis tells me the dominant noise source is the shot noise from the drain current, and this shot noise increases with the square root of the drain current, exactly the same behavior as if the transistor was a BJT.  For a drain current of 5mA, the noise from the GaAsFET is only 4 times less than with a BJT with the same current, while I expected a reduction of at least 15x.  Can anyone tell me if the noise analysis for a GaAsFET is generally accurate?  Thanks