This only explains that you mis-use the controls and enforce a variable fixed point encoding mapping. If the min value determines the position of the decimal point, then really the 0 value can not be used. This would imply, that the gain is LINEAR, starting with 1.000 ratio as the minimal gain, but also mean that you can not set less than 1.00 gain (e.g. 0.5, as some sensor support that as well). But the IMX185 driver does not use LINEAR gain, it uses LOG gain, in units of dB. And discards the fractional part anyway, due to poor coding.
The documentation (screenshot you posted) is unclear in what units the gain really should be - whether LINEAR (ratio) or LOG (dB), and does not specify how to handle missing codes, when the sensor can not be set to an exact gain.
Every sensor we have worked with, being that with integrated ADC or external one, the PGC stage has a finite amount of gain settings, ranging from as low as few steps to few thousands and the values are rarely continuous in linear or log space, sometimes even multiple values map to the same gain. This shall be handled by a LUT, with gain ID and gain Value and not by an imaginary fixed point number of an unknown unit, that was designed by someone who never worked with an image sensor.