I'm seeing the same thing. This is definitely a bug in Asiair. I just took a series of images with N.I.N.A. at different gains and the EGAIN values from the FITS look much more reasonable that what I get out of Asiair.
These are the gain values from the Asiair's FITS:
EGAIN = 3.1800000667572 / Electronic gain in e-/ADU
GAIN = 0 / Gain Value
EGAIN = 1.00560426712036 / Electronic gain in e-/ADU
GAIN = 100 / Gain Value
EGAIN = 0.100560434162617 / Electronic gain in e-/ADU
GAIN = 300 / Gain Value
And here are the (presumably correct) values from N.I.N.A.'s FITS:
GAIN = 0 / Sensor gain
EGAIN = 0.76800000667572 / [e-/ADU] Electrons per A/D unit
GAIN = 100 / Sensor gain
EGAIN = 0.242862924933434 / [e-/ADU] Electrons per A/D unit
GAIN = 200 / Sensor gain
EGAIN = 0.076800003647804 / [e-/ADU] Electrons per A/D unit
GAIN = 300 / Sensor gain
EGAIN = 0.024286292493343 / [e-/ADU] Electrons per A/D unit
GAIN = 400 / Sensor gain
EGAIN = 0.007680000271648 / [e-/ADU] Electrons per A/D unit
GAIN = 500 / Sensor gain
EGAIN = 0.002428629435599 / [e-/ADU] Electrons per A/D unit
GAIN = 600 / Sensor gain
EGAIN = 0.000768000027165 / [e-/ADU] Electrons per A/D unit
GAIN = 700 / Sensor gain
EGAIN = 0.000242862937739 / [e-/ADU] Electrons per A/D unit
